The real problem with these cutter bars is they do not have a way to check the correct oil level. You drain them and then put back in a measured amount. Not enough and they will ruin the bearings or too much and they will blow the seals when they get hot.
I would bet that if you contact Kuhn they can get you a operators manual.
KUHN NORTH AMERICA, INC. - 1501 West Seventh Ave. - PO.BOX. 0167 - BRODHEAD, WI 53520 - Phone: 608-897-2131- Fax: 608-897-2561
Also I would find out exactly where you are leaking oil. Even a small leak on these can be disastrous. They do not have much oil in them to start with.