I hope the pictures work.....
Is this the chaincase drainplug, on the underside, on my "51 A7 Plunger?
If it is, there is a screw inside the bolt. Is this the drain and the larger one the fill level?
Looking in the inspection hole there seems to be plenty of oil in there, but oil constantly weeps from the next cover screw on the left, under the bulging bit. (It's been leaking for a year or more and should have emptied itself by now?)