Convertible liner

[studio945]

I have a 2004 325cic. I noticed recently the appearance of some sort of mineral deposit on the interior liner of the soft top. It looks kinda like a meandering white line of salt deposit on the very back of the liner, just below the back window, and two additional lines behind each of the rear side windows.
If you went half-way into the ocean, up to the middle of your pockets, then came back out and tossed your shorts aside to dry, when they dried you'd probably be able to see a line of salt across your shorts marking the water line of how deep you went in. The deposits on the liner in my car look just like that, but I'm not sure
1. How it's getting there and if it's presence means I have a leak problem
2. What exactly it is ("road salts")?
3. How to clean it without damaging the liner. A cloth wet with water alone doesn't seem to do it.

Thanks!

[mankiks323i]

its probably dried up soap from the carwash and possibly hard water deposits . unfortunatly covertables are not water tight no matter what the car is. not sure how to remove that

[shamilot]

How many times have you washed your 325Ci? How many hours has it been out in the rain? I can't imagine that water would seep through the fabric in less than a year, unless "you went half-way into the ocean, up to the middle of your pockets, then came back out" in it.