The distributor seal (I think that's what it's called) is the the back of the pump, basicly the casting the injector pipes bolt to has a round sleeve going in to the pump, you can wind it out just far enough the see the seal and stretch a new one over and on. If you go too far I believe the whole lot falls apart!
So if I recall correctly, you take the air cleaner barrel off, and the (lack of) vacuum pump off.. Actually it was the loft pump. I dont have air con.
Injector pipes off. The position of the pump was important, so there is Spring weight on the distributor head as you wind it out, otherwise bad things can happen. Wind out the four bolts carefully (make sure you have a good quality hex socket, they are tight initially and if you strip a head...) until you can just see the seal. Whip it off, the new one will stretch over the distributor head, I wrapped tape on the rough bits. Reverse process it back together. Like I said there's a good tutorial on one of the Vw forums, maybe even on YouTube actually. What I've said is an overview. It wasn't hard job, tough on the lower back:)
Cleanliness is the word of the day.

