oil leak from prop shaft housing on ulster

[Venn]

I'm a relative beginner here looking for advice.  
I acquired an Austin 7 Ulster built in 2000 from my late father and I am refurbishing it to put it back on the road after a 20 year lapse and I am on a very steep learning curve. I drained the differential oil out and refilled it with EP 140 oil 3/4 of a pint as recommended in various threads. The car is on rear axle stands with the front wheels chocked on the ground. A considerable amount of oil is leaking from the propeller shaft casing through a hole which deliberately seems to be placed in the bottom of the casing about one third of the way back from the universal join to the diff casing. Should this hole have some sort of plug in it? It seems to be deliberately placed there but if oil is simply going to leak out of it from the differential I don't understand quite what it is for. Whilst the back of the car is higher off the ground in the front, this would happen going down any hill so I can't believe that is the problem.  I have a Box saloon 1929 which does not seem to have a hole in this position. The other difference between these cars is that the differential is much wider on the saloon and quite narrow on the Ulster.
I would be grateful for any advice about how to proceed. I have taken a photograph on my iPhone but I am not quite sure how to attach it to this thread because it tells me it is in the wrong format. 
Thank you to those with expertise for your help in advance
Peter Venn

[Terrytuned]

Venn the torque tube has a breather on top of the torque tube yours could be fitted upside down, the hole should have a breather plug fitted. The banjo axle (3 piece ) has a breather pipe fitted to the top of the diff housing, I don't have a photo. Terry.

[Reckless Rat]

With the rear of the car on axle stands the angle of the torque tube is allowing the diff oil to run forwards and out of the breather hole which shouold be on the top. Take the car off the axle stands and it should be OK. It is probably overfilled as well, 1/2 pint is usually enough.

[Erich]

Peter, I'll add to the great advice of the two previous posts, that too much oil in the differential housing can cause the oil to make it past the hub seals and end up on the brake shoes...not very good if you want to stop.

Erich in Mukilteo

[Bob Culver]

I take it the Ulster is in name only. If the diff casing itself is narrow presumably it is the wide track post 1933 D type. If indeed reversed I think thr the torque tube can be rotated. Others may confirm. Six bolts need to be removed. Great care taken to observe where any shims fell from and must be arranged to allow free reentry of the bolts and no dirt. 
The torque tube ball may need adjusting to free.

Rotated torque tubes have arisen before Can wear of the front ball of the torque tube be somewhat countered by reversing? For those not previously reversed, a new hole could be drilled before reversing.

My Hillman car has a mere  unprotected hole in the top of one axle tube as breather....