Hello all, I am looking for some advice on what oil to use in the transmission (21+ liters) and rear axle (41+ liters). I bought this tractor to bushog my 10 acre field and it has done a great job so far, but I am wanting to service it so it will continue to work for me a long time. Both the owners and service manuals recommend the same lubricant type and SAE grade for both sumps. From +10F to +90F a "mild EP SAE 90" lubricant is recommended. The Ford spec. is M-4864-A. The brakes on this are external disc with brake pads, so no worry with wet brake compatibility. When I smell the lube that is in there is smells just like hypoid GL5 oil (strong sulfur smell). I also know now after reading that the rear axle oil is also used as hydraulic oil to raise and lower the lift arms. There is a hydraulic pump in the bottom of the rear axle. Should I go back with a 75/80W-90 GL5 gear oil, which is readily available and not too expensive? Or do I search for some special Ford type Mild EP gear oil? This tractor only gets used in mild to hot weather, so I even considered mixing in some 85W-140 to quiet down the somewhat noisy gears below me. The books actually say to use SAE 140 lubricant in temps above 90F. Will I harm anything by using a GL5 gear oil instead of some special Mild EP lube that may not even be readily available? I have not even considered using synthetics in this due to the age of the unit and the leaks here and there on the rear axle (at the rear wheel seals and PTO shaft seal). Also it gets worked hard only about 3 or 4 days a year, that's it. This tractor is my first non-automotive vehicle and I'm still learning how to use it and service it. I just figure that some other BITOGER may have more experience in this area to give me some advice. I am open to suggestions and instructions. Thank you all in advance.