I've used a lot of stuff over the years.
I agree that cerakote isn't as wonderful as many people seem to claim.
Norrells Moly is the best spray on finish I have dealt with. I've used it for more than a decade and for one example, this spring, I refinished an old mossberg with it after I cut the barrel down mainly to seal it off to oxygen and the elements.
It has hung on a nail in the barn (no air conditioning, no heat) just wide open outdoors of living in the south most of the spring, all of the summer and so far into the fall. Temp swings have so far went from 18*F to 103*F with about 3000% humidity.
There has been 1 spot of rust come up on it at the handguard nut. I put some motor oil on it and rubbed it with a rag and it came off and has yet to form back.
I carry it to the cabin and trail camera sometimes a couple of times a week. Enough so that the OD green camo spray paint is wearing off of the stock and you can see the tan stock color showing through underneath.
But the black moly paint on the barrel and receiver is still holding strong.
I abhor the aluma-hydeII from brownells. It's garbage. KG GunKote and Cerakote are both similar. Duracoat is pretty durable but takes a friggin' week to cure enough to touch it and put it back together. Plus it applies pretty thick so it's not going to do well on slides and frames. Spray paint does "OK". The good thing about it, it can be touched up whenever you need to without needing an airbrush and an oven.
I've done a lot of stuff, but blueing and parkerizing is probably the best, but norrells works the best from my experience. It's also very heat resistant. I use them on my gun silencers, which can get pretty warm.
As for cleaning old oil and solvents. Brake cleaner if you can put it on bare metal where you don't have to worry about plastics and lacquers melting. Otherwise, I use alcohol or acetone, depending on what I'm cleaning. It evaporates pretty quickly, and doesn't really leave a residue. But if you can heat the parts up for a while, you'd be surprised how much old oil and gunk can stay hidden in places you can't see or reach.