Thanks for your reply, MAS985. Hmmm...

Well, the pump & filter system is probably circa 1980 - or at least mid-80s.

I had the motor/impeller assembly apart a few weeks ago. I got the impeller to turn by hand; it seemed to turn freely. I carefully re-assembled it and did not notice any leaks under the sump.

Still and all, your suspicion about the bearings may be on the right track. Perhaps they should be replaced.

What I was mainly trying to figure out was whether the motor's cutting out a couple times/day was normal. You seemed to think not. Duly noted.