I have no definitive knowledge as the only kick start BMW I have is my R100 which is effectively a /7 and I do know that the kick-start arrangements differ (in ways I can no longer recall)between "round" and "ribbed" gearboxes.
That said, I would remove the kick lever and have a look, BMW were once pretty good and making arrangements for minimal structural disturbance for service items, so I would strongly suspect that the seal will be removable from outside.
My main reason for this post is that the kick-start oil seal does not normally get enough of a workout to ever leak, if you have been using the kick start a lot I would suspect that the kick start shaft has worn the alloy in the cover plate which in turn has allowed enough lateral movement to do the seal a mischief - if so, merely replacing the seal will only provide temporary relief, the cure will be to have the shaft bore bred out and a bronze bushing inserted, a simple task well within the capabilities of any machine shop worthy of the name, the problem is of course that in order to remove the cover plate, the gearbox has to come out.
