Here is a message from someone on YTMAG. Also Bush hog has a website.
I bought a DM80 this winter at a auction. Paid 250.00 dollars. Put all new seals in and it has worked excellent. I would make sure oil level is good in all gear pods and run it. You should also make sure the break away hitch is adjusted and working properly. This is very important because if you hit something things can happen real fast. I bought a owners manual from brush hog for 12.00 dollars and it had a lot of good setup info. There is also a dealership on line that was very good for parts. I think their name was Meesick's.
That was one of my questions, does each individual disc have an oil resivior. i see a bolt under them that looks like it may be a place to add oil. The gear box was low on oil when i bought it. i took the vent bolt out and it apears to have a dip stick on the bottom of it with two marks on it i assume are the low and high marks. I added 90 weight until it reached the line. I will look online for the manuals. Thanks for any input.