The Rodenstock is a PIA to get started, but once you break loose the front beauty ring the entire front cell screws right out. Same with the rear cell. If it is really stuck, I would suggest gently warming the outside of the housing with a hair dryer. Hold the lens securely with something like a padded vise or a lens board. I have placed mine in the jaws of a six-jaw lathe chuck covered with tape to protect the finish.
I find that having a very secure way to hold the outside of the lens is as important as finding the right rubber to turn it. A collection of different sized O rings is what I use. Viton material, wash it with detergent to give it more traction and clean any oils that might make it slip.