Hi Steve
The reverb pot is actually not sealed and can be opened with a bit of persuasion! Be careful though, no mole wrenches etc. You have to unsolder it and then hold securely. I used a vice with protective jaws and then gently working around the circumference with a tool of your choice it will pop open. Once opened you can see the condition. In my case (A122) all that was needed was a spray with Servisol 10 (USA DeOxit) ?It will then work perfectly for another 50 years or more!
Good luck
Robin (UK)
