How do I unstick a stuck retaining ring?

[Mackinaw]

Any suggestions on how to unstick a lens retaining ring on a Mamiya 80mm TLR lens? The shutter is sticking and I need to remove the rear lens group so as to access it. Problem is the rear lens retaining ring is stuck. I have the proper lens spanner and no matter how much torque I apply the ring won't budge. I've tried applying a few (carefully) applied drops of Liquid Wrench to the threads to no avail. I've even tried heating the ring with a hair dryer. So far, nothing has worked. Any ideas as to how to unstick this retaining ring?

Jim B.