BP....the way you describe the symptoms of varying speed on one of your VPI's sound like belt stretch to me. Try boiling the belt/installing a new one/switching to rim drive. Just trying to be helpful.
on the point of having manufacturers (or even stores) keep in touch with their valued customers...nope - has NEVER happened in the 50 years or so I've nuddled around with this stuff... However, if ever I had an issue/question/comment,... any need I had was quickly addressed with VPI (Harry), Vandersteen (Richard himself, and John Rutan of Audio Connection) or Ayre (Michael Weidemeir). No ...not even one complaint the way I've been treated.