There is a slight leak from the rear axle. Enough that you can see a blob of oil on the floor where he’s been standing for a while.
I thought I’d check that the vent wasn’t blocked as this can cause pressure to build up when the oil warms up but I can’t fine one. There is no mention of one in the workshop manual either.
Do they have a vent? Where is it?
It’s a very small hole , on top , about half way down the tube ,
I fitting a bigger breather , with a one way valve !
That looks like a Land Rover Series vent cap.
Sadly I have been unable to locate the vent hole.
I have scratched away for ages with a bent coat hanger (a tool everyone should have 
) but to no avail.
I will have to visit my brother, who has a two post ramp so the axle will ‘droop’ and maybe I will be able to see it.
I’m guessing you only want to install the breather when the axles are apart due to swarf…
This is how I did it , sorry about the music , I cut the clips to fit the music , Holst , but because of copy rights , had to change it 
I have found, and cleared the holes on my XKs. On one car it was totally blocked, perhaps causing a leak on the diff. The holes are on the right side of the diff, on the top, about 10-12 cm from the diff. Very small holes.
On one car there is a wet spot on the front of the diff casing, just above the middle, and close th the centre.
As ifthere had been a hole, about 7-8mm which someone (or the factory) had welded to seal…Very strange
