A reminder that DIY doesn't always go easy, sometimes its a swine.
Double glazing is maybe 30 years old and a second lock/gearbox has gone. Remove DG panel, to allow some flex in the frame, still an absolute swine squeeze a hooked implement into the gap, find the mushroom head peg to release the window. Lots of swearing, got it, then it fell into place again and locked, gah, repeat process....all to get the gearbox out, measure, find one on the Internet then put it all back together. Repeat process when the new part arrives.
Scarred the frame, damaged the gasket, its not always easy....and I've done it before, it went quite well that time.
Ah well, they are 30 years old, no surprise bits are giving up now.