I'm working on a friends 112 RP 65. It's a GP-3A version, with the 6L6GC tubes.
The reported faults are: "as some buzzing whenever it's on, the volume stops increasing after you've turned to maybe 4 or 5 and the reverb doesn't work at all."
I suspected filter caps before opening it up and, sure enough, the 2 x 100uF/450V caps in the dog house are bulging.
I'll also replace the other filter caps too - 2 x 150uF/50V and 2 x 400uF/25V. I may or may not replace the other 7 x 20uF electrolytics (might as well while the board is off).
The question I have is - what's going on with those rubber bits on the +ve end of the 400uF caps?