My Mk2 is a bugger to change gear. Have used different oils and this makes no difference.
If I go down to first gear I always hit neutral when changing up to second, and I have to give it some real welly to get into second. Changing up into third doesn't seem so bad though. Havn't gone much higher, because racing under hare and hound conditions these arn't normally required.
Don't know if my clutch is adjusted correctly, and would this make much of a difference, as "clutchless" changes should be possible anyway?

Any help, greatly appreciated.

clutchless changes are no problem with the Mk2 , easy way to check clutch adjustment with the engine stopped stick the bike in gear and try and push it , if the clutch is adjusted correctly it will be easy if its not correct it will be hard to push

You probably have worn parts in the gearbox. Either the ends of the gear change dogs or chipping on the slots of the drum. Parts are relatively easy to come by 2nd hand if you keep your eyes open, but you will need to split the crankcases if I'm correct.