Unfortunately , these plugs should not look like this . I would think the oil is getting past either the intake valves or the piston rings . The least expensive step would have a competent shop to disassemble the heads and check the intake valve guides for too much wear . I do not think these bikes use a valve stem seal . You would have to check a parts manual.
If this checks o.k. , then it is time to re-ring the bike . If you hone the cylinders , you can hone with a ball type hone for just a few seconds because these are a nickasil coated bore.