I painted mine with 2 pack laque.
No primer, no nothing, just a quick wet sanding as preparation.
No problems with peeling / fading / yellowing since then ...
I have a spare set (4 pcs) of chromed ones.
You interrested?
I just had them soak in some (initially hot) dishwater for a few days, then i rubbed them with a sponge (the scrubbing kind). The corroded top layer kind of dissolved in the water, what was left were 4 new looking doorhandles. You might give that a try too!
If they are chromed ones, they will polish nicely with ordinary chrome polish.
For non-chromed ones, I use Permatex Plastic Cleaner (it may also be available from other makes).