904 tailshaft mystery leak.

Looking at it again, where the spray pattern up in the tunnel is, I would say it is the tail seal that is leaking even though new 2 years ago.

That slip tube on the Yokes can have rust pits in them from over time. They can have a groove cut in them too where the seal runs, both causing slow leaks.

Sometimes you just have to put on a new yoke/slip tube to get a new sealing surface for the tail seal. New seal too at the same time.