I tried every soak I could and had very little success. A drop of Liquid Wrench, a few taps on the lens to set up vibrations, repeated three times over 12 hours, and then a steady pressure with rubber gloves for about three minutes (seemed like forever) finaly got some movement. After disassembly, a little naptha took the residual Liquid Wrench off and I put one drop of a teflon based lubricant back into the threads with a small brush. Seems to have worked.
Mine is a Solinar. Once I got it working it showed itself to be worth every one of the $25 bucks it cost me at the junk shop.