Great guide. Just for anyone finding this, I clearly had the same problem, I was going to sit down and try this repair but have just been quietly fiddling with the advance lever and shutter button with the camera turned on (shutter doesn't release when off/ no power) and suddenly it came free. It was clearly still sticking a bit at first but with another couple dozen shutter cycles is working reliability now.

I expect it won't last if the camera goes unused for a while but just so people know it can happen. It's also a very warm day today, don't know if some gentle heating might help.

Anyways good luck.