Interesting google searching this, it appears the problem is widespread and I ponder whether Celestron or Meade warranty tolerances of mirror flop or shift? One poor guy had to re-focuse a C11 when he slewed more than 30 degrees!
http://astroshed.com/observatory/c11saga/c11saga.htm
Was the best article I read, where the guy dissambled everything twice using advice from BinTel tightened collar and finally tried a violin wax / vaseline grease on the main focus tube to reduce mirror wiggle!
Amazing that this isn't just machined far more precisely, or they use PTFE slides or tiny ball bearings between focus tube and mirror cell to eliminate all wiggle.
Surprised there isn't a buyer beware or notice of tolerance that should be achieved else you send the OTA back for a service!
This is also a good read:
http://www.astronomiainumbria.org/ad...sh/lx_flop.htm