Right about the pto seal if it leaks just transfer oil from one side to the other.
The o-ring on the mounting flange suppose to keep oil in tub of tractor.
This Oring rarely just leaks usually from installation malfunction .
A good rule of thumb for oil leaks keep looking up till things get dry.
People on here seem to not want to explain their problems so makes it hard to offer a fix.
So the more story you print the better we can help.
Bob

Correct, neither side should have pressure. The winch fill/full plug is below the PTO shaft level.. Check transmission dip stick for fill level.

I have an older Hyster D7D (mechanical) on my 59 D7. My experience with that winch to mount leak is because that particular winch is always spinning if the main tractor clutch is engaged and its the mechanical shift on the winch that is in neutral. I am not sure of the 7E is that way and only uses hydraulics to shift verses the fender mount 3ft lever on the D7D. My point being that that rather large and expensive bearing on the winch shaft can get "loose" and rather raise heck with a seal that is 60+ years old. Yes I have the winch off and replaced both the bearing and the seal (Chicago Leather is no longer around). It is quite the effort to get them changed with the hardest part trying to align the pto spline that is deep in the machine with over 2000 lbs hanging. Nearly impossible to get a hand in there and extreme care must be taken when trying to achieve that initial engagement.

Hope this helps