As previously mentioned my Gearbox is being refurbished at present, a quick examination by Charlie Skinner @ Cloverleaf Transmissions highlighted the following points, apologies if you folks know this detail already
From the image attached...
1/ The rubber bushing at the base of the gear leaver has a metal tube running through the center, this has to apparently be free to spin within the bush, in the case of my box this was siezed solid, according to Charlie this was the major contributing factor to 1st & 2nd jumping out under load.
2/ Where the shifter arm joins the selector from the back of the box, on my box was very loose/worn, this will be replaced and should give back a better overall feel to the gearchange.
3/ Rear mount/bush, this is worn and will be replaced again giving a better feel to the change.
The internal's have yet to be examined but they will be stripped out with any worn parts replaced, I'll definatly have a decent box for next season, possibly with a slightly longer second & third which should suit Knockhill better.