I've been granted permission to use some info from this site at the bottom..thought I'd share the wealth and I have more to follow..
The care and feeding of the leather and the vinyl components of your automotive interior are two very different processes. If you are using one product on both, that is somewhat like using gasoline as a lubricant. It will work, but not for long. I will cover the care and feeding of leather and vinyl separately.
Leather having once been used to keep the insides of a cow from falling out was designed to pass moisture through tiny pores. These tiny pores absorb human perspiration and as the water evaporates, salts contained therein remain to absorb the essential oils in the leather. This accumulation of salts and other grunge should be cleaned from the leather about twice a year (more often if the seats get more than their fair share of your leftover sweat). The loss of oils within the leather is the first step to hardening, cracking and shrinkage. Leather dashes are very prone to this problem. Your dash is subjected to the destructive UV rays and heat concentrated by the windshield. The leather (or vinyl) of your dash rests upon a metal backing that acts like a frying pan. This "frying" drives the essential oils from the leather causing premature shrinkage, cracking and hardening. Thus a dash should be treated more often than the seats or door panels.
Cleaning leather may be accomplished by using a mild soap and water, or specifically designed leather cleaner. Of all the products I have tried, I still like Lexol pH Cleaner. It is pH balanced, and gentle. All cleaners will rehydrate the leftover salts and grime and wash them from the leather fibers. Use only leather products on leather, do not use vinyl cleaners, as these products tend to be much harsher and may not be that beneficial to the leather. Any cleaner should be rinsed thoroughly from the leather. I have tried spraying off with a hose, but that just seemed to fill the car with soapy water (a hole drilled in the floor was needed to drain it out - just kidding). I went back to using a damp cloth and repeatedly wiping down the leather. Once the leather is clean, a conditioner should be used to restore lost oils and emollients. Envision leather as a sponge. When the leather is new, the "sponge" is full of oil and soft and pliable. Body salts, UV, heat and other factors drive the oil from the "sponge", allowing the leather to shrink and become brittle. A quality leather conditioner will help maintain the oil in the leather. There are several conditioners on the market. My favorite over the years is Lexol Leather Conditioner. It seems to be the most easily absorbed into the leather fibers and tends to leave a relatively less "greasy" finish than any of the other products I have tried. Another good product is Connolly Hide Food. This product is made from rendered animal parts and will turn rancid in about two years. This and the distinctive "cow" smell removes it from my top two list (I spent too much time milking the south end of a north pointing cow, so am not a fan of cow smells). Zymol makes a product called "Leather Treat". It does not, in my humble opinion, do any better job than the much less expensive Lexol. One Grand Leather Conditioner is a petroleum-based conditioner that seems to work better on the American and Japanese leathers. Again, do not use a vinyl product as a conditioner on leather and above all try to avoid raw silicone oil based products. The silicone oil will dissolve out the leather's natural oils and tend to make the leather sticky. Silicone oil has a very high electrostatic attraction, so will invite every dust particle within miles to set up camp in your interior. Apply the conditioner to a soft cloth and work into the leather, allow to be absorbed into the fibers and then buff off the excess. You may condition the leather as often as you wish. As a rule, condition your leather 3 to 4 times a year. The leather will tell you if you apply too much or apply to often. The leather fibers will just not absorb the excess.
If your leather has hardened or needs some intensive softening, there is a really nifty product called "Surflex Leather Soffener". This product is made from natural and synthetic oils that restore the natural softness to neglected leather. Clean the leather and then apply a liberal coat of Soffener and cover with plastic. Allow to penetrate the leather for at least 72 hours. Wipe off the excess. If it needs an additional application, repeat the above. For really bad areas, cover with plastic and allow to sit for a few days. Once the leather is sufficiently softened, allow to "cure" for another 24 hours and buff off any excess. You are done. I jokingly say this product will turn a dog's rawhide chew into a kid glove. I have had some luck with leather dashes with this method. Once the leather has softened, I have been able to gently tuck it back under the edges of the trim and windshield clips. This is a lot cheaper than a new dash and may be worth a try before spending a ton of money.
If your leather or vinyl has scuffmarks, scratches or areas that the surface color has been removed, you may refinish it yourself. Most German seats are famous for scuffing on the left bolster of the driver's seat. This is usually caused by your belt loops as you get in and out of the seat. The key is another Surflex product. The Surflex Colorant & Finish for Flexible Surfaces may be matched to the exact color required. Any interior leather or vinyl surface may be refinished. It is not recommended to spot finish any area. If your seat bolsters have belt loop scuff marks, you should refinish the entire front of the seat. I usually do from welting to welting. This provides a visual break that does not make the non-refinished areas appear quite as shabby. But then why not do the whole seat, dash, or door panel? Start by conditioning the leather to insure that the leather is fully hydrated with oils. Once the leather is fully conditioned or softened, if needed, then clean the area(s) to be refinished with a suitable Organic Solvent. I prefer P21S Total Auto Wash or Wurth Citrus Degreaser. Prior to usage, test all solvents on an area that does not show. I use the excess on the underside of the seat to test the colorfastness of the finish. Spray the solvent on a soft lint free cloth, and then wipe down the surface(s). Repeat after a few minutes. Rinse several times with a sponge or cloth and a couple of buckets of clear water and allow to dry thoroughly (at least 24 hours). The manufacturer of Surflex says to strip the old finish off using lacquer thinner, commercial paint remover or C-P Stripper. I don't, because most interiors are not in that bad a shape and I have never found it necessary (They also recommend lightly sanding the area prior to usage, I don't do that either - no guts). Mix the Surflex completely and apply with brush, spray it on or use it like a wood stain. I prefer to use a small piece of lint free cloth and work the Surflex into the leather or vinyl just as if I were staining wood. Once the desired color of finish is achieved, allow to dry undisturbed for at least 24 hours. I allow the surface to "harden off" for about 6 weeks before applying any conditioners to leather or vinyl protectants to vinyl parts. I have not had a lot of luck refinishing dark leather to a significantly lighter color. The old color tends to show through in small "cracks" and the whole panel seems to be "muddy". Maybe if you strip off all the old finish, it would look better. Someday, I will get an old seat and give it a try.
The Surflex Black Colorant works great on black bumpers, black spoilers or black rubber/vinyl trim that has been severely scratched or badly scuffed and is beyond the help of Black Again. Clean the entire part thoroughly with P21S Total Auto Wash or Wurth Citrus Degreaser, rinse and dry thoroughly. Mask off the paint and then stain the area with the Colorant and allow to dry. It will look like new. After about 3 weeks hardening off, coat with a protective coating of Black Again or One Grand Exterior Rubber.
Small cuts, cracks or holes in leather may be partially repaired using another Surflex product called Flex-Fill. This is a semi-flexible cosmetic filling material. You use it like a Spackle compound. It will take the Surflex colorant similar to leather or vinyl. I have been able to repair several damaged areas and hide them so they are not visible to the casual observer. Will it make a three-inch crack in your dash look like new? No, but it may help hide it so that it isn't quite so obvious. I have found that forcing Flex-Fill under the repaired area and forming an inverted T patch works best. Once the patch is dry, sand lightly to blend in with the leather or vinyl. Clean the area thoroughly and refinish with the Surflex Colorant. This is a learned skill, so you should practice on a test piece of leather or vinyl. Perfect your techniques before you tackle your expensive interior.
Car Care Specialties, Inc.116 South Main StreetLodi, NJ 07644-2251(877)796-8300 www.carcareonline.com