I'm with you, Ace: the small scales do seem to need more attention to track cleaning. Incidentally, I have made a track cleaning car in 0 and S, following your suggestions. It's amazing how well they work, and I want to thank you.
Michael, I have noticed that the grease in Z-scale engines will cause the whole mechanism to bind up tight if they are not run frequently. Could that be your engine's problem? Of course, maybe somebody used too much current trying to get it going when it was bound up, and ruined it.