So, got on and removed the selector shaft from the gearbox. The bearing was toast as expected, but the unfortunate news is the selctor shaft itself is heavy pitted and gouged from running on a knackered bearing and water ingress. Got a brand new one coming, so things are on hold until then. Little photographic how to below, but it goes basically like
1, remove clutch cable to gain access to 27mm hex cover, which means, operating the clutch lever on box, clipping the white retainer to kepp the clutch cable tensioned, remove retaining clip rubber from cable and pull the cable out.
2, remove nut holding linkage to selector shaft
3, remove 27mm hex cover, big spring behind so be sure to get it.
4, possibly the scary bit. Removing the top detent bolt, if you have a late box its 24mm and is kinda like a ballpoint pen arrangement. scary part is it can come apart as your removing and sprinkle hundreds of tiny ball bearings into your box. As you can see it came out in one piece, but fell apart in my hand! lucky!
5, the shaft will now slide out towards the radiator.
6, with a suitable drift knock the old bearing out towards the cab.
7, press in new bearing from the cab end. i used a long shouldered bolt and a couple washers to wind it in.
Thats where im up to now, couple pics of the knackered shaft included. More when i get the new one in.