Does anyone have experience working on CD Jukebox(s)?

Back in '97 I bought one (Technics SL-MC50) with 0 + 60 slots. Usual
practice was to screen a CD in slot 0, then move it to a slot in the
1-60 range as part of a permanent library. I'm guessing the unit
hasn't averaged 3 hours usage per year since I got it.

Yesterday I put a new CD in 0, the unit repeated an internal check 3
times, and returned "error" (no code).

I pulled it from the system, work-benched it, pulled the cover. Clean
as a whistle, absolutely no apparent problem. When I tested it, it
worked OK with several CD's in slots 1-60.

So I lubed it a little, inspected closely, re-tested (OK), and put
it back in service. It played several CD's in slots 1-60, but when
I re-tested in slot 0, it did the internal test and yielded the error.
Now I can't get it to play anything.

Something to do with slot 0.

Any idea what might be involved?

TIA,
Puddin'

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."