I removed the lip that the gaiter sits on first as I wanted to keep that, so proberly about an inch and a half.
I kept the lip and glued it to the shaft butted up against the base of new nob. This has worked perfectly as I wont have a problem with the gaiter slipping down and you cannot see the lip as the gaiter covers it and the base of the new nob. Quality finish.
On the subject of all things Gearbox, I was reading somewhere though I cant remember which lounge about a gearbox additive to improve shift, I could do with this as am not overally impressed or should I change all the gearbox oil (done 64,000).