Has anyone had experience or see the need for a breather to be added to the rear end of T's ??

When you think about a freshly overhauled unit with double O Rings & Seals on the safety hubs and sealed bearings in the upgraded drive shaft bearing area they are now a lot tighter in terms of leak points.

An ideal spot would be on the top of the left tube towards the outer.(or RHS for Australia) Any thoughts?

Alan in Western Australia

Some people think it's a good idea. Any heated up pressure in theory, squeezes out some grease thru the hubs. My had a vent added by the re-builder. Simple hole with flap type oiler cover to vent. A 71 Torino that I inherited had a vent and tube going somewhere. Guess Ford thought it was a good idea on the modern cars.
George n L.A.

Any change in pressure will go out/in through the pinion bearing, up/down the torque tube,..........

See above.

The most important reason for having a Differential breather is if you are going to be driving in water. When a hot (or warm) diff hits cold water, it creates a bit of a vacuum and will suck water into the axle bearing, if you are going to vent it, it is a good idea to have a bit of tubing that is anchored to a high spot on the frame to avoid drawing water into the vent.
Best
Gus

I did it once on one of mine. Rifle drilled one of the upper spool bolts. Then I decided that what Ken said was right and it was not needed.

Drive lines with open drive shafts are in need of a vent as they have a seal where pinion shaft exits the diffy. Enclosed drive lines normally do not have this seal allowing pressure variations to normalize through the drive shaft tube.