Clean it real good with rags and lacquer thinner.
Then sand with 120 grit or so.
Find all the cracks and "V" them out with a hack saw blade.
Fill the Vs with PC-7 and let cur completely.
Then re-sand to smooth out where it's filled.
Make sure the transition is smooth and flawless.
Primer. Base Coat. Clear Coat. Good auto paint goes a long way here.
This is what I did to turn a giveaway POS 47 Ford wheel into the a pretty good looker. Took an evening and morning.
Before with tons of cracks that don't really show in the photo and nicks too:
After:
