[OM] Viewfinder problem

[mms]

Zuiks,

Using a recently bought OM-2, I noticed that my 50mm lens would focus beyond 
infinity.  Must be the lens, I thought, but it works fine on my other OM's.  Do 
I have a mirror offset of some kind?  Loose prism?  I can't see any way to 
adjust the mirror stop.

I was focussing on some Mtn. peaks about 20 mi. distant, which is about as 
close to infinity as it gets around here.

Any ideas?

Morgan