removing a nikon 300m from lens board?

[stradibarrius]

I have a nikon-m 300mm f/9 lens mounted on a Sinar 4x5 lens board. When I mounted it I only tightened it by hand but now I cannot get the retainer ring loose. Nor will the rear element loosen. I know I did not over tighten because I was afraid of damage. does any one have any ideas as to how to remove the retaining ring. I do have a lens spanner wrench.
Thanks

[hoffner]

A drop of oil behind the retaining ring and your spanner wrench will work miracles.

[dodphotography]

I have a nikon-m 300mm f/9 lens mounted on a Sinar 4x5 lens board. When I mounted it I only tightened it by hand but now I cannot get the retainer ring loose. Nor will the rear element loosen. I know I did not over tighten because I was afraid of damage. does any one have any ideas as to how to remove the retaining ring. I do have a lens spanner wrench.
Thanks

I was forced to bring mine into a local shop (ep levine) who took about 40 mins trying to get it off without damaging things.

[stradibarrius]

I had a bright idea and used a "strap" wrench on the rear element and that did the trick.
thanks for the help.