Possible Causes Of Oil Leakage Through Oil Seals

Hello friends,

I have a problem with particular gearbox, in which the oil leak is unable to arrest, even after replacing the oil seals and oil seal ring. The leakage is happening through the oil seal of the input shaft. I doubt the following causes:

1. mis-alignment of the driving shaft. But this is a propeller shaft with 2 UJ's and in that case, the mis-alignment not seems to be a valid reason.

2. Improper mounting and vibration. I am unable to validate this cause. I have seen the similar gearbox with same level of vibration, where the leakage is not there.

Can you suggest any other reasons/remedies for this problem?