Toluene/Toluol (harmful)
Xylene/Xylol (harmful)
Ethyl acetate (less harmful)
Acetone (I haven’t tested, yet…) (less harmful)
MEK (harmful)
any “cocktails” (different brand names) based on the above will all melt styrene.
Test with bits of sprue to check if it works or not.
My eyes were opened when I had bought a bottle of lacquer thinner, it smelled strong
so I checked with some sprues. No god for painting but good for “glueing” styrene.
It thinned the paint alright but the thinned paint would have destroyed the plastic …