i dunno if it's "correct" or not, but i've found that starting fluid and mineral spirits are both great solvents for cleaning up oil. i'd hesitate to set the disks on fire, cause you don't want to warp the steel part. maybe just make sure it doesn't get too hot.
if you get all the free oil off the surface, i wouldn't worry too much about the oil that is soaked in, at least on a "working" tractor. the brakes might end up being noisier than with new, clean disks, but they'll work ok.
you can see your friendly CNH dealer or aftermarket such as a&i for a brake seal kit. there are two big o rings, 1 smaller, and a lip seal for each side.
make sure to check out the self-adjusting screws, that the tab prevents them from backing up and that they turn freely.
also check out the 4 return springs- they can loose some of their spring with time and heat/cool cycles.
as for the pinion shaft, can't help ya, never had any trouble with them.