Loose image when focusing
The focus knob can have the play reduced. Turn counter-clockwise a turn or 2, then loosen the knob's set-screw and carefully turn clockwise until a little drag is felt. Then tighten the set-screw.
A further item that may pertain to image shift, especially at low powers, is that the baffle tube that the main mirror slides on, may be loose in the back housing. There have been reports of poor thread engagement due to poor tolerences. That tube can be re-tightened - just be careful not to strip the threads!.