Mine is a little later model than that, but it leaks on the backside, where the right hand shaft comes out to drive the header auger.
On edit: I am repairing mine right now. It is leaking behind the inside sheave. The dirt is absorbing the oil, so it doesn't make a mess. I think the problem is the vent plugged up.
On edit: I am repairing mine right now. It is leaking behind the inside sheave. The dirt is absorbing the oil, so it doesn't make a mess. I think the problem is the vent plugged up.