So, as advised, I cleaned the switches with deoxit and worked the pots a heap. That pretty much resolved the obvious issues. Thanks for the tips xwarp & tautech.
I set about calibrating it as per the manual. Someone has had a crack at that (badly) before I reckon. It was starting to look good. Then it stopped.
Inspecting the power supply revealed r661 (+55v) and r641 (-110v) had burned and been replaced. r641 was well toasted again. Replaced it. r651 (1r, +12v & scale illumination) was toast too, by design, it appears to be a fuse. Replaced with a jumper and the scope is back to life.
The unregulated voltages I measure are on the high side. Mains here is 230v, and that is how the transformer is wired, but the manual does have details for wiring it for 250v. I wonder if there would be any benefit adapting it to 250v? The regulated voltages are pretty good.
I was having a browse through the schematics to see if I could see anything that might obviously overload those rails. Nothing stood out. Advice appreciated on this front.
I also noticed that r475 on the sweep generator was badly burned, this is a divider for the external blanking input I think. D476 seems fine, so someone may have just (well) overloaded it in the past. I will replace it at some stage.
Now, I have another issue. This might be ignorance on my part, but channel 2 does not seem to invert symmetrically. With channel 2 ground coupled, trace positioned on the centre line, the invert switch moves the trace by a whole division. This might go away after I calibrate channel 2, but I'm not sure I want to go to all that trouble only to do it again if this issue is somewhere on the input amp. Again, advice appreciated.
I updated the first post with my current issues.
I have to say that having the schematics is quite a treat. So far this has been fun; and the scope still makes me smile.