Hi folks, I have a 1963 Fender Deluxe amp, the grill cloth has some fairly minor stains (probably from spilled beer) plus the accumulated grime from having never been cleaned in the last 44 years. I bought it new and in all other respects it is immaculate. Does anyone out there know of a totally safe way to clean it? I'm afraid to try in case I make it worse. Suggestions???