I've owned one for 20+ years. The poor thing has been treated roughly. It has "mowed" some trees that should have been cut with a chainsaw. After about 10 years, the oil level in the gearbox had to be topped off each use. There is a lower seal on the output shaft. Getting the blades off this unit is a cinch. Getting the crossbar a little harder. When I tried I came to a washer that was welded over the seal, so I gave up on changing it since I didn't own a welder at the time and carrying to one would be a pain.
I just fill it up each time. By now, it leaks pretty bad so I pretty much have to fill it every use. Last year, I tried a tip from an old timer and packed the case with grease. This worked pretty good but if you operate for a long time, the grease melts and leaks out anyway.
I still use it to bushhog about 80 acres a year plus making or maintaining trails in the woods. It has been a good one for me. I am looking to get a larger one, 10 or 12 footer, pulled type for open areas. After I finish all my hogging this year, I'm taking it to a shop for major overhaul, adding some heavier deck and side plates (after the sides are straightened ). I will reserve its use for brush and woods work and let the big one deal with fields and pastures.