Also Welcome to OCC!
Since it sounds like you are new at this situation, I'll offer some suggestions.
First yall need a bath to get off the mud and crud to see where you are bleeding.
No need to start sewing up what appears to be a cut when it is just an old age wrinkle, or hemorrhoid's
All that said, normally a person cleans the hydro & differential casting up with your favorite parts cleaners and or power washer.
When it is clean then you can begin to see where it is leaking, ( prolly like my old 1956 Harley panhead did when I was a youth)
sometimes it is as simple as the relief valves leaking and need rebuilding.
or the oil filter is leaking, or the suction tube got damaged or as Roland mentioned, the cork gasket.
Then again it could be the expansion plug just under the cork gasket.
or the 4 seals on the hydro.( 3 of which can be replaced from the exterior)
The 4th, seal, the hydro comes completely apart
The last thing a person should do is take things apart and shotgun parts at it
guessing where the leak is.
Oh, if you narrow it down to a specific area after a thorough cleaning, you might want to sprinkle some of your favorite powder on the area and it will reveal the exact leak,-- as gravity plays tricks on people.
Any powder will work, like baby powder, monkey butt powder, baking powder,
Pillsbury flower, clabber Girl powder,
( none of that J&J powder that causes cancer ) well you get the picture.
