Worn gearchange splines
 

The bolt holding the gear change lever vibrated loose on my lc4 resulting in the splines wearing badly on the leaver and the output shaft. By tightening the bolt back up I managed to be able to change gear this may last 10 miles or 10,000 miles. Is there anyway of fixing this without replacing the output shaft as i suspect that this will be an expensive job! (obviously i will replace the lever ASAP.)

you could try this:

With a metalsaw cut a wider pinch gap and replace the shifter bolt with a higher grade bolt. You may even want to use a nut and bolt comination. You can then tighten the shifter against the shaft.
If the splines are really dead, then you will eventually need to replace the shaft