I went ahead and removed the A1 board, and replaced all the Caps. I've been slowly putting everything back together for the past week or so, including gluing up the fan mandrel that (like many others) broke on removal.
I rather tentatively powered the 'scope up today and ... got a weird readout screen and no main trace.
I powered down rather gloomily, but checked my work and found that I had misfitted one of the IDC connectors from the front panel. Corrected that and ... things are looking good!
I will probably post a photo or two after I have cleaned up the case a bit and fitted the scope back in it.
One thing ... now that it is working again, I am reminded that one of the front panel LEDs doesn't work (Channel 1 input mode 'DC' indicator). I assume it would not be much of a job to fix that? Any pointers to replacements etc.?
Oh, I had (only!) one screw left over ... one of the short 1/4-inch Torx screws. Not sure where that might have come from, I'm toying with stripping it down a bit one more time to find out..
Cheers from the UK, Jon N