On your fan I am sure you already know its a Sauer-Danfoss at Home - Sauer-Danfoss
dealer is Hydraquip in Houston, Texas 713-680-1951 and Berendsen Fluid Power in Little Rock, Ark 501-490-1091
The latest Sauer/Danfoss number is 121.20.045.00 and the descripyter is SNM2NN/017BN06GA Gear motor keyed The old descripter was SNM2/17 CI06.
All this info comes from the Monacoers Forum Parts file in the file section.
Have you tried your local Hyd motor repair shop, it probably only a seal replacement but will probably have to come from one of their dealers if i remember right I think they are a bastard size.
Ray AW46 as Moisheh has posted and some had Dexron III