Pretty straightforward Alistair. Easier than playing with Burmans. Did one the other week (one arm on the spring had bust, same as Bill's), and - if that's all that's up with it, it's pretty easy. Just whip off the outer, and you can do it in half an hour if there's nothing else funny in there. Drain oil, have usable gasket to hand or paper to make one, replace spring and cover, refill with slime, and job done.
I bought a couple of spare springs while I was on . . .