I purchased a Sears treadmill at their surplus store one time, an expensive model. The service contract was based upon the purchase price, and inexpensive. That treadmill burned out and they replaced it with another expensive model. Over the years I paid and they repaired and replaced 4 or 5 times.

I can tell you that the motor control boards are what always "went", and they would replace them as long as they had them for that particular model, and then they'd replace the treadmill.

They never did try to repair one. On the other hand, those repair guys were real generalists, and didn't have a lot of time to screw around.

And that's all I know.