Right Channel dropped out Bryston BP-26P (upgraded from BP-25P)

Long-time member/reader, first time poster  Moved my speakers to new location (used Cardas recommended measurements per post I read today on AudioGon site.  Long story short, turned on system, no right channel.  However, balance ctrl in center, I have left channel output in both speakers. Balance Ctrl fully to right channel...nothing.  Same whether it's switched to Mono or Stereo.  Found negative spade connector off on right speaker (did not seem to be touching positive terminal.  Reconnected still have the problem  Using Bryston 4Bcubed amp.  Both channel lights are green so I don't think it's the amp.Suspect preamp is taking a trip back to Bryston. However, also saw a post that said to clean input selector contacts, which I can do? Any suggestions welcome.  BTW  It's out of warranty