Acetone is suggested. This coin had slime but not the damage I have seen on others so I decided to try what was at hand since I have no acetone. I do not know if the coin would be different now if acetone were used. I probably would not have bought that coin had I seen it at a show and have very little experience with PVC. I was surprised that the situation was not worse considering the time the coin had to be in the holder. Are their different levels of PVC in some brands of holders so this was less affected than some or was the fact that those years were in a dry part of California more of the reason? I do not know. Dealers who handle thousands of prior collection coins a month probably know these things.
I've never tried rubbing alcohol, but apparently you were successful, and one can't argue with success. Acetone is easy enough to acquire, however. The paint supplies aisle of any hardware store will do. I've been told you should avoid nail polish remover because of the added color and/or fragrance, but I guess that depends on whether you want your coins to smell like coins, or roses.