Thanks Dale, I'll try a hybrid and see how that works. I don't have it in Red but I have some in something else and I'll make some comparisons with some other types. Yeah, I think you are right about the epoxy, a friend did some gas caps in epoxy and it's chalking a little after a couple of months.
Oddly enough, I tried some samples today of the polyurethane that I had trouble with, at 10, 20, 30 and 40 minutes. All of them showed good resistance to aviation fuel afterwards, so maybe tavo1765 is correct in that the original parts might not have been fully cured.
Powdercoating is so cool, it's hard not to take stuff out of the oven, I just gotta look at the finished product
But I'm getting better at leaving in to fully cure.