Fairly typical, condensation or something. You could flush it with kerosene or diesel, if there is no harm in doing so, seals or what have you.
I welded a hook on my rhino SE-6, and use that to hoist it and place it upside down, to drain the oil out. They are a bit awkward to handle, but with a loader, and carefully rigged, it should not be too difficult. You could use a siphon of some sort, but I preferred to drain mine, it gave good results, as the lube stays clean now.
This one pressurized this year for some reason, so I kept checking it, releasing the apparent extra oil, I thought it was water as I usually service it once a year, but having done so in the past, the oil was clear, clean and either I overfilled it a tad or what, its pretty simple with the level plug, just not like me, maybe it was not level, they don't hold much. It was hard to believe it was overfilled, now fine, thankfully I kept releasing the excess every few rounds. This older one has no vented fill plug. So most of the excess ran out, I kept checking as this can make the shaft seal fail if I read it correctly, this one calls for 18 ounces of NLGI 000 lube,(Alamo Part No. 00765444) I could not find it conveniently last time it was serviced, so I used a Lucas 80W-90 or 90Wt, I forget, no problems, been at least 2 seasons since it was changed, probably cut 10-12 acres or so per year.
Some never service these, often times like a differential, I don't subscribe to that, they don't hold much, upside down it all drains nicely, inexpensive lube change, mine was coffee color oil, seems to stay clean now, next season I'll put new blades on and service it again.
I don't believe tube or any similar grease is really meant for these, people do it when seals fail, some swear by it, its splash lube in my eyes, designed to have a specific lube, per the book on mine, NLGI 000, and or corn head grease would be similar, maybe even the old crawler track roller grease stringy like bar oil. Tube grease settles out, soap base and oil with age, that will make a mess inside a gear box, in my humble opinion, if a seal goes, why not just fix it, these are not complicated to repair. On mine, the stump pan comes off easily, then the gear box, could be on the bench within an hour.