Polystyrene as well. Acquired a Dragon32 recently and spent a few hours digging the power cable out of the polystyrene. It had melted it's way through about 3cm. Horrible clean up.
All those people storing their retro "treasures" MIB complete with free chemical reactions ruining it.
Ugh. Decaying rubberized surfaces that turn sticky are a nightmare and it goes beyond retro and vintage gear to equipment still in current use that may only be five or six years old. As of yet, I've found no way to treat or clean these surfaces once they start to go.
Impossible to clean since the problem isn't that they're dirty, it's the rubber degrading. I've swapped out analog sticks on ps1/2 and gamecube controllers about a dozen times by now. Unfortunate thing is the build quality of most of the replacement parts I've been able to find have them turning sticky faster than the original parts.
All those people storing their retro "treasures" MIB complete with free chemical reactions ruining it.