I will check it out well tomorrow, but the oil isn't perfectly clear but doesn't smell like engine oil, maybe it is picking up some of the dirt in the bottom of the housing before leaking out? I also noticed it leaks the most after driving it continuous for a quarter mile or so, but not so much if i am just working it around the house, so it appears to leak alot more if the wheels are turning alot. I will check the vent as well tomorrow, and report back.
Engine oil is pretty black. Even just changed it picks up micro soot from oil-wet surfaces and gets black quickly. Front driveshaft seals are a more likely source, given your symptom and the amount of owner experience reported on this and other forums.
The original seals were prone to leaking - some dealers started doubling them up, putting two lip seals where the shaft comes out of the transmission.
There was also tube spacer added (170 on attached) running thru the clutch housing to hold the seals in place, and with o-rings on each end. This should have helped keep oil out of the clutch housing - but later seal changes were needed too.
My rig didn't leak before the split and doesn't now - I did noticed the front driveshaft tube was full of dark grey grease surrounding the shaft. MY L48 WSM doesn't mention the spacer or putting grease in the covers.
There are quite a few fwd orange tractors out there that develop leaky front driveshaft seals - some respond to adding the spacer on tractors that didn't have it (there's a service bulletin for it).
Take care, Dick B