Re: Gear Lube
Look at page 5A-2 of the manual link I gave. It was either a vent, or not used.
Now, check your pump again, by the looks of the rust in that hole, it doesn't go into the reservoir, just to the top of it, so it shouldn't be your problem. Besides, if the oil was coming out of it, or the water was getting in, the oil level wouldn't be low, it would be full.