you must have a really thin finish.. my bass is 31 years old and ive been gigging while its in my possession solidly for the last year or so. and i play metal so i sweat a lot.. its got more belt buckle rash than anything. id try and maybe clean it with windex and see if that gets rid of the dirt. if not you might just have to live with it unless you want to strip the guitar naked and start over....
bassist for the crux
Randall RB-125-115 120 watt 15" eminence spk.
Randall RBA 500
2X Acoustic B115's