Some good suggestions that might help me make progress... and an interesting observation that the chassis metal is really too thin :(
However the end of this email is heading back to the "diagnose it yourself" department which was so unproductive the first time round.
I was sufficiently encouraged to reply the same day with some of my own suggestions for shipping - see part 18.
If you were to ship the chassis, I would first wrap it in cardboard. Then seal it in a plastic bag. Then pack that with at least 50mm of padding (Styrofoam sheet material or bubble pack material would be preferred). I would not send the cabinet. You could pack the reverb pan with the chassis, just to make sure I have everything.
The chassis thickness is thinner than it should have been, so the chassis can be damaged if the amplifier is dropped. Therefore, shipping just the chassis is better.
Still, I think you could get proper function by replacing some of the plug in wires. RR2 (Reverb Return Two) and one or two other wires would be what I'd check first. I'll make a list and get back to you with that.