Hi Peter B,
I have checked the spring and the horizontal locator pin........ All ok, no cracks present in the hat either and no signs of anything out of place thisside of the cases. I rang Gas Gas UK and I was informed of some link in the shift drum that may have gone caput, as all else has so far failed they suggested to check this. Apparently the top hat should break if the gear lever is knocked, so the job is easy to do but sometimes this link bends or breaks instead and it is a bigger job. I shall strip the old girl and see if the problems are further inside. Thanks for the advice so far it has been a great help in eliminating other possible causes.
Where's my spanners...................?
P.s. The spring on the hat is a bugger to get back on! I see why it comes ready built.
TTFN