I see two holes.
I'm guessing from the postition of the left one being higher, this is where you would add gear oil, until it would come out of the one on the right.
Doesn't appear either hole has had a plug in it for a long time.
The little gearbox probably full of dirt.
Just guessing.

Them holes are to put the tine cover on with bolts and nuts. Here is the same picture but has arrows drawn to show where the hole is.

{{gwi:304074}}

It looks to me like the chain has worn a hole thru the case!!!
Mike