None of the above. The problem ended up being a clogged drain line. A straight pin got stuck across a reducer that had been put in the end of the drain hose and collected a bunch of lint. I removed the reducer (a barbed nipple that had been hose clamped into the end of the drain tube) and the pin and lint plug fell out. Fixed.
On the bright side, I've got a new pump and belts on washer.