swing and a miss!
Ack! I ordered a RPM sensor for my Sears unit today off eBay. Cheap gamble, $12 with free shipping. Looking at my unit on the Sears service site, it could be that, the main board or the limit switch. I guess the capacitor is a works or not works deal. Both of mine work intermittently. So I'll try the new part in each of them to see if it cures either.
I noticed that new units are in the $200 range.. plus I'd have to pay them to install them since I don't have experience doing it, nor any help. Probably should just do that, but the stubborn fools we are.. we just have to fix it!