Lock loose gear shift levers by welding a nut to the boss, drilling through the boss, then tapping for a toothed grub screw which bites into a seat in splined shifter shaft. I've done this to nearly every bike I've had or looked after, especially the ones which "go down"...

http://www.facebook.com/album.php?aid=2013877&l=67070&id=1126907019

Looks good
Had a had few problems with worn splines on gear levers, while on the road I have bought a pack of sewing needles and jammed some between the gear lever and shaft works for a while but can be a problem when you drop the bike should also keep some spare needles if you need to do this. I did not want to weld the lever on because of the seal and did not want to be drilling into my gear lever when far from home.