I ended up cutting two slots in the retaining rings to get a spanner in but that still wouldn't do it even with heat so I ended up denting the retaining rings in with a pair of pliers and pulling them that way. There was about 1inch of threads, the penetrating oil had saturated all the way through but the brass is so soft that it was just flexing and jamming when I tried to unscrew it. Got the elements out, and working on recementing the front one. Should have a working lens by tonight.