I learned from a Chemist on another forum a trick for restoring old plastic car parts.
If you boil water on the stove or your microwave, remove it, and then drop the parts in they become pliable. Somehow it affects the molecules and sort of restores the plastic.
Shown below are two 1969 Ford Torino spot mirror gaskets. They were very hard from years of use. As you can see after several cycles in the boiling water I could twist them.
I have tried this on allot of small parts and it works great.