[Penthode]

I dissolved the rubber with water. The rubber was totally rotten on my set and I ended up removing the coil and putting the picture mask in the bathtub to soak and remove all the gunk.

Mine was goo and after removing the brass trim, I slowly was able to pull the outer glass away. But the black goo mess I think can only be properly removed by taking the picture mask out and soaking it in water.