Is there a certain procedure for fitting a kickstart to a 2007 sherco 290. dont really know how to fit the ball bearing, spring etc.......

With everything cleaned, fasten the lever upside down in the vice, put the spring in the angled hole and the ball on top of it, use a bit of grease to hold them in position, then firmly push the bottom piece of the kickstart into the hole until it goes fully down, then finally insert the grub sreew with some thread lock, this should be tightened till it touches the bottom then backed off 1/2 a turn so the kickstart can swivel easily

I've had an o-ring delivered with mine, should that be an o-ring or a washer?????????

O-ring