Well, it's been a year and a half but figured that I ought to update this thread since I dug the scope up a couple of weeks ago and finally did the repair. I also want to say thanks to rf+tech and mij59!
mij59: Great, that was exactly what I needed. Finding a replacement wasn't that hard after all, I just had to click the link!
Fixing the latching mechanism did not pan out so I ordered one from Conrad. Thanks buddy!
Shock: There appears to be a few versions of the PSU and mine turned out not to have Rifa smoke bombs. The last image of the PSU board in my post was borrowed from another user and is a slightly different version than mine. I used that before I had taken a look at my board.
rf+tech: I took the switch apart but didn't see anything broken or missing. Sure sounds like impressive machining you did on your switch!
You were right regarding the electrolytics and the whine was gone after replacing almost every one of them, and a bit of noise that were in the trace disappeared too. Mine doesn't have that brief whistle/whine you described and I wasn't even sure that it powered up the first time until I looked at the front and saw the LCD was lit.
I started by lifting legs of a few caps and measured high ESD and decided to just replace the whole lot. Once desoldered I then measured all of them and almost all were bad, the exception being the the two high voltage 68µF cans and the two metal can 6800µF/10V axials mounted as radials. ESD measured in the hundreds of Ohms on some and a few were in kilo Ohms, and they had lost up to 90%+ capacity. At that point I got a bit impressed that it did work despite those caps, apart from the whine, and would guess that it must be a pretty good design since it tolerates such out of spec caps.
I ended using a bulb for the graticule illumination but used three LED's for the LCD lighting. I like the result and prefer the cold white for the LCD instead of the incandescent used originally.
The plastic in front of the LCD was warped and had two annoying drops of what must have been super glue. I replaced that with a cutout from a random but scratch-free plastic clamshell pack. Unfortunately the blue CRT filter has a few drops of super glue too but I can't seem to find any blue 2 mm perspex, only the standard 3 mm that everyone has. If anyone knows of a source please share, I could use some for other instruments as well.
I found something odd (to me) that I'd like an explanation to. The following image shows a series of 110 Ohm (0.6 W I think) resistors in the finay Y amp circuit that get quite hot, judging by the discolored PCB. Why this string of resistors, that apparently aren't big enough to handle the power, instead of say two 330 Ohm? I'd guess this is a possible future point of failure?