I had the same problem. I have the same car and sport seat as you. I found a tip that really worked for my seat. Buy some Lexol conditionner. This stuff is the best to use to condition your seats. You put it on wet, leave it for 10-15 mins and the seat looks almost dry because the seat just soaks up the Lexol. Now on to fixing your problem. Go to a local shoe repair shop and buy some black leather show dye. Take a small amount of the dye and mix it with some Lexol in container. Then take a rag and apply it to the problem area of the seat. Because the Lexol absorbs into the leather so well, it sucks the dye in as well. Leave the seat to dry for a little while and then buff the seat. Before you sit in the seat wipe the area with a cloth to make sure the dye is dry.
I agree with the previous post in that using a company like Fibrenew will make your seat look brand new again, however, the dye method is a quick fix that really works well.