That's a tough one. I used to be a big fan of Viking lines but have been hearing a lot of things regarding their quality as had been mentioned on this thread. Amsteel has always been a good brand too and I might give them a try the next time around.
Can't speak to Powerplants, but I've seen an M8000 fail. Uncle gave me his recently, which I've rebuilt and put on my bumper now (see pics from my Wave intro).
Autopsy revealed the main bearing in the motor failed and the armature came in contact with the wiring. Lotsa molten copper inside. (Incidentally, insert shameless plug for a battery cutoff switch here). Further investigation showed solenoids were pretty rusted and very close to end of life. Gears were in great shape, but looks like my uncle had taken them apart recently and regreased. Unfortunately, he used gasket sealant instead of ordering new gaskets. This was a fairly old winch, mid-80's serial number.
I've rebuilt it with new gaskets (took the blasted gearbox apart THREE TIMES before I had it back together correctly), sanded and repainted the drum (brake was in great shape) and replaced the motor with a 6hp one from that shop up in TN. Now it's a little closer to a 10k winch in power. I also replaced the solenoid pack with a Chinese contactor in the Albright style and a new cover. Also put a dyneema 3/8" rope on it from OK offroad.
It's a machine and can fail, like any machine. But I'll grant the M8000 is a tank. Having poked around in the motor, I would still be real hesitant to dunk it underwater.
Cheers,