The neutral switch is a common source for oil leakage.
If you tighten the switch with a wrench, and 'snug' it up a bit, there's a good chance that you have damaged the switch.
It will work correctly, but usually it will start to leak through the switch body itself.
I was told by a local independent shop, to tighten it up by hand with an oil resistant sealant on the threads, easy to do with the gearbox removed from the bike, not so easy to do with the gearbox still on the bike.
Back to the original post, the metal clamps that secures the rubber boot, can cause problems itself, stripped threads due to to overtightening, also there is a channel shaped piece of metal that bridges the gap between to two 'ears' of the clamp, this is tack welded to the clamp, if it is missing, good chance it will leak there as well.