sounds to me like someone got to em with some acid at one point in time and thats probably the only thing that will clean them again OR you can *try* this. go with some lacquer thinner and a goof stiff brush should do the trick if you dont want to try acid. acid will clean them but you will more than likley have to use it from now on. good luck trying any kind of diluted crap you will buy at a parts store, youll probly or already have wasted your money.