I've now rebuilt my shifter, those links were a big help.
I bought a 2nd shifter- (an ebag bargain shipped via Andy N, ta mate) and I went through both and decided to select the best parts from each to make one goodun.
There were no breakages and both units were working, but some parts had lot of wear and both needed a thorough clean.
Stripping them is pretty easy. Just pop off the stainless dust cover and the pressed steel side cover and wiggle the guts out.
Normally I'd have to leave myself detailed instructions and photos of where and which way round every part fitted. Instead, I just played the youtube links on my laptop as I rebuilt it and had no problem at all

Some thing's weren't as clear as they could have been so I've put some photos here to clarify.
No-one will believe you...