I use
Shell Rotella T 15W40 (engine)
Shell Spirax HD 80W90 (both diffs/tranny)
NAPA AW46 (hydraulics/steering)
ISO100 compressor oil (injection pump)
and Slick50 "One Grease" because of it's universal compatibility
There are actually three drains up front; the main one is in the center of the axle housing, the other two are on the underside of each drive hub. It comes out slow, so it's best to drain while what's in there is still warm.
If you can't find out from the previous owner, I think you should assume that it's never been flushed either. It's very important to get all the manufacturing and break-in residue out of these things before it's given a chance to do any harm. If you're unfamiliar with flushing, it's a widely discussed topic here. The search engine will turn up lotsa info.
//greg//