[Al Skierkiewicz]

Bob,
Mark has some good advice. Although I have never changed the FETs, what you describe sounds like a combination of a large thermal mass and holes that are too small for the leads. It is possible that the board was drilled for the right lead size but never compensated for the plated through hole.
As far as the fire and flame from the controller, let us know if you find a bad motor. Most often, it would have left evidence in some other way like driving problems. You may have a thermally induced short. This is where wiring breaks down under high temperature. You may have a wire in the motor that shorts when the motor gets hot but is fine under test in the pit. The phenom of one FET blowing after another is normal as the shared load gets dumped on the remaining FETs or the dead one produces a short on the other two. High junction temperatures inside the package cause the case to crack open. The light (arcing) you see is the FET trying to turn itself into an LED as the silicon junctions break down one after another. I love the smell of burning silicon in the morning.