hi again,
this seal is under the brake pressure which taken directly from the boost pump pressure and fixed at around 20 to 25 bar max, it would be worth checking this for pressure spikes although i would expect this to affect both sides. There should be no high pressure into this area from the motor side as it normally goes into the leakage system and through the cooler and return filter into the tank. I suppose you could check the leakage line from the axle for blockages.

The seal will be affected badly by bearing wear on the shaft support bearings, are these OK? Is the half-shaft worn in the seal running area and the shaft pushed fully home.
The outer half shaft bearing is only grease lubed so can wear out and the leaking oil will wash the grease out.
I suppose you could have been unlucky and just got a duff seal!
If you need more info let me know. I was the hydraulics designer for the old Boss firm and still have a few contacts.