Alternator Issues

The windings are the least likely what is wrong so you should not have to separate the casing Just make sure theres no mud and grit in there. Yu can hose them out with clean water and dry them in the sun or with an air line.
Carefully take the carbon brushes out and give them a good clean. They are very delicate. If they look well worn then fit new ones.
Once again very carefully clean the copper rings where the brushes run against.
Dont use anything sharp as they are very soft. I use a plastic washing up pad and plenty od WD40.
It could be the regulator but these are not repairable as far as I know. You would have to get a new one.

Success! Cheers for your help on this one Shifty - I'll buy you a beer if I ever bump in to you!

The bushes are quite worn but I was able to move the thing a little futher in and tighten the screws up. Everything got a really good clean, dry, and spray of WD40 for good measure. Reassembled it, stuck it back in and it works perfectly now!

I called 3 or 4 local garages, and also Rimmer Bros, and no-one does replacement bushes, nor can they get hold of them! The answers were all "we just fit a new alternator". Shocking! I'd be pretty ****ed if I'd been charged £130 or so for a new alternator, for the sake of a tiny part (pictured)!

There are plenty of places that refurb alternators and starters. They get the bits from somewhere. It's a bit like bearings. They are available but need some detective work to find out where.
Find a local refurber and they should be able to order you the new brushes for a small consideration. Since I've moved house my "local" is some 30 miles away in Earlsfield but is worth his weight in gold. He wont tell me where he gets his stuff from but for the price of a few beers on top of the cost of the parts he is happy to order them in.