[Arran]

Before you strip the cabinet try some automotive cream hand cleaner like Gojo, it will remove a lot of the dirt and wax and will at least give you an idea of the proper colour scheme if nothing else.
With regards to the tube socket that is clear evidence of a excessive current load in the B+ circuitry caused by a short circuit. I would check the speaker field, output transformer, and the power transformer with an ohm meter to see if you still have continuity. If the speaker field is fine then the speaker can be reconed if need be. There are two solutions for the speaker if it needs replacement, a P.M type with a filter choke attached as a substitute for the field coil, or another electrodynamic speaker.
Best Regards
Arran