Thanks! Seems like I eventually get to join lots of clubs: first the F40 Wire Routing Club, now this one. Took the locomotive over to my LHS yesterday and Brian said he's seen lots of issues like this. Sometimes its the gears, sometimes related to the motor shaft. He's going to take a look, but not 100% hopeful. Maybe I'll be looking under tables at train shows for an old post-war rectifier frame and trucks.