It uses engine oil. Having had to rebuild mine, I suggest draining the old oil out every couple years. Previous owners apparently had not checked it often/ever and since it is not sealed enough moisture had gotten to make a real mess.
As far as the rebuild goes I did mine myself. Do you have a repair manual? It's fairly helpful, but I ended up doing some minor modifications to mine. If you're not interested doing it yourself, there are a couple TBN members who offer parts for these. They frequent the Satoh section often. One is lens12 (sheaf tractor) and the other is BillRogers (valley equipment). IIRC is spoke with Bill when rebuilding mine and he was helpful even though I ended up buying all the parts I needed through a local industrial supply house. (One advantage of being an mech eng is knowing how to spec and get things like bearings, seals, etc..)