I recently sold a Nikon FM2n on "The 'Bay'" that I'd used without any problems for years. Listed it as near mint condition. The buyer, at follow-up, stated that he took the camera to a reputable Nikon repair shop for a check out and they found that the mirror was loose. They charged him $45 to tighten the mirror and "refocus the camera". I've never heard of refocussing a camera body. Does this make sense to anyone, is there any consequence to not tightening the mirror? Is there something that can be adjusted in regards to focus within the camera? Thanks for any info.