Chances are is is just leaking around the boot. If you look at the mating surface of 'Leaky' one you can see the thick glues of fucking silastic that the factory started using around the rectangular 'Compression plate' that holds the front of the boot. This started being done some time around the beginning of 2010 to prevent exactly the sorts of leakage from the clips on the swingarm you've got.
The problem stems from the 'Compression plate' relies on being squeezed tight into the boot recess on the front of the box to prevent oil leaking past the boot edge and into the arm. The problem is it isn't very good at it! The result is oil seeps past the boot and plate and then, because the clip holes go all the way into the void in the swingarm oil will pool and drip out.
By slathering a gallon of silastic around it they can virtually gaurantee the boot won't leak and therefore no drips from the clips. The massive pain in the arse is that the silastic renders the Bevelbox virtually irremovable from the swingarm. You have to use a bottle jack between the bottom of the suspension linkage and the ABS sensor mount to lever the bugger off and then the 'Compression plate' which is retained to the box by two self tapping screws, will tend to bend as it tries to remain attatched to the swingarm! Grrrrr! You have to get in with a screwdriver and lever it off before the box will separate.
I prefer NOT to glue the box on with silastic for this reason. Sometimes they're fine. Sometimes they're not. While it could
be the pinion seal I doubt it is but what I'll do is take the compression plate off and then glue up the boot with some Threebond on both sides of the boot lip before re-installing the 'Compression Plate' and then I'll run it on my bike for a week and see if it cures the problem. It usually does. If it doesn't then it is
the pinion seal and I'll have to take the box apart to replace it. Only good thing with that is it gives me the opportunity to remove the pinion nut and tab washer and Loctite the buggery out of them like I did mine after the pinion nut dropped its preload. It won't be happening again on my bike!