There have been plenty of times when replacing a hose where the machine has dumped alot of fluid and i ran out of hydraulic fluid that i filled the rest with 15w40. John deere uses 15w40 for hydraulic is some of its machines. I wouldn't fill my bobcats system up with motor oil but if you get some cross over from attachments here and there its not going to be catastrophic..we have several brands from bobcat, deere, tak, kubota and they all call for there own blend of hydraulic. But they all get used with the same grapples, mowers, planner ect. Never been an issue for us. We fill all machines when repairs are made or hydraulic fluid gets low with a universal hydraulic fluid.. I honestly don't think there are many fluids out there these days that fall short of meeting manufacturers requirements if its a high quality well known brand. Of course some dealer supplied fluids have their on special blend of 7 herbs and spices. We dont use them and our machines get run hard, put up wet, sometimes not even put up at all and its never been an issue for us.