Tried a search but didn't find help.  The AO bell is extremely stiff,  I can barely move it.  Lock ring is removed.  Any advice on how to free it up??

I'm assuming it is old gunked lube in there.

Be leery of applying penetrating oil to the threads to loosen them up. I always feared the stuff migrating onto the lenses. That said, I've used small drops of lighter fluid as a thread un-locker on scopes and a couple old Leica camera lenses that were bound up from stiffened lubes. That is not a sound professional recommendation - do so at your own risk.

If it is tight in both directions then something is in the threads and have gummed things up. If its tight just trying to unscrew it, there is a chance that the lens holder has either shifted or was not lined up with the guide pin and causing problems. If you can remove the lens holder then its an issue with the threads.  There is a very small pin like protrusion that keeps the lens holder from turning and you need to be careful when putting that back in so it is aligned correctly.
Sam

Just a thought, solvent used to clean refrigerate system expansion valve screens is very quick drying and leaves zero residue. Nothing to migrate. I use it on many gun parts. You have to be quick as it evaporates rapidly. It is available from AC/Refr. Wholesale suppliers.
Mike

heat as mentioned does work, blow dryier but dont over do it.

Heat should be the least invasive. I’d start with it before lube and only takes a few minutes to see if it works. If at end are you sure you didn’t get a cross thread?

This is a grease we use in vacuum system where out gassing is an issue (the grease does not vaporize).

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