Hope you can get it sorted locally Paul. The capacitor that's broken off is a filter capacitor, there to reduce noise on the preamps' power supply. On clean, vintage amps like this it won't make much difference if disconnected.
If it's not sounding right, could be any number of issues.... most common are valves, leaky signal capacitors, and open circuit resistors.
It will be worth much more working than not. If you don't get sorted I can put it right (Newcastle).