Okay, I think this one is a success.
I ended up removing a lot of the components, they were just too corroded to recover. I have access to an ultrasonic cleaner so I ended up putting it through that for the max time. Thankfully the main transformer didn't have any glue on it and seems undamaged, the inverter transformer did and the fragile windings made it difficult to get the glue off the legs, but I got it pretty clean. Could always replace it with an LED backlight if it fails eventually.
I've attached a spreadsheet with all the components I've replaced in case it helps someone (lists capacitor pitch / diameter etc). Also just a warning for anyone working on one, the
primary side heatsink is live, I know it's common, but just thought I'd point it out.
Surprisingly it still works with all the new components populated. I was a little worried I'd make a mistake due to the amount I was replacing. I've run the scope for a few hours now and haven't noticed any issues.
I also upgraded the firmware to V1.11 and ran the vertical calibration. GW still provides the firmware on their website, but I'll attach it here too so it's backed up.
It seems to be working properly now, and it's nice that it's a four channel and 200MHz, but it's a shame the screen is so low resolution. You can see individual pixels easily.
Also, I was curious and opened up the front end acquisition section:
I also took the front panel off. The Ch 3 LED (LED1703) was blinking occasionally and I wanted to check there was no conductive epoxy on the front panel PCBs (there's not luckily). The LED for Ch 3 had some black marks on the back of it, I think it might have just been sharpie though, it cleaned off with alcohol easily. I re-soldered it again and it seems to have fixed it, maybe just temporarily though, I guess it might have broken bond wires internally?