Welcome to the forum.
In regards to the TRX400FA's and parts, Honda only made them for 4 model years, and they are one of the more poorly considered Honda utility atv's they have made. I'm one of the last regulars here with one. BUT if well maintained and if you don't over-exert them, they can last just as long as any other one. They share a few body and chassis parts with the 2005? on up Rancher 350's, but it is limited. Otherwise they are kind of their own thing so getting parts will get tougher, which is usual. Thankfully for you lots of them were abused and the hondamatic went out early in its life, and was not worth replacing so the rest of the atv was parted out. Seem to be quite a good selection of good used 400AT parts out there.
What I have decided to do to hopefully extend the life of mine as long as possible:
- no oversize tires. Stock 24" are fine. I run 23" though.
- Rotella T6 5w40 oil
- manual fan switch to keep it running cool and because if the oil temp sensor goes out, you won't know it cause light won't come on and neither will the fan.
- don't overdue it with heavy work. We do deer food plots but use our tractor whenever possible, and I use my Grizzly 450 whenever we can't get the tractor there or for pulling the harrow and sometimes small cultivator or packer.
- clean the oil cooler often with a pressure washer. even without mudding, dust will eventually clog it. and even with a clean oil cooler and fan running, mine still feels like it runs hotter than any other air cooled honda. There is a lot demanded from the 3 qts of oil in these things.
What was your system voltage when the machine was running with the new stator? If it was over 14.5 volts, that could mean your regulator/rectifier is bad, and it is allowing voltage to be too high which causes the stator to fail.
X2 on this. Don't just focus on testing the stator itself. Run through the regulator/rectifier tests as well. You don't have a battery that is toast and needing a constant heavy charge, do you? I almost thought I needed a stator at one point, found an aftermarket one available.