[OM] Never-ending OTF and 300mm f/4.5

[Greg Heier]

I have an OM-2 (1976) that sometimes exposes forever when in auto. I need to 
set it back to manual to stop the exposure. It always works fine on manual and 
most of the time (maybe 19 times out of 20 or more) on auto. Any ideas on what 
this might be?

I'm thinking about purchasing a Zuiko 300mm f/4.5. What should I look for when 
evaluating condition of a lens like this? Any caveats specific to the 300 f/4.5?

Thanks in advance!

Greg