Probably going to piss some one off here, but having issues with those that claim they know versus those that actually know.....Here we go. I've got three Ferris walkers, two DDS units and one single circa 2002. All have been outstanding units. My deal is this, the single drive has no filter, pretty much a sealed unit but has had the fluid swapped out four or five years ago. That was done with hydro fluid, not SAE30 engine oil. The DDS units now need their fluid swapped out, but several service centers claim SAE30 engine oil is what they use for fluid replacement. The service bulletins from Eaton mention hydraulic fluids for their transaxles.....but nothing definitive. Listen, engine oil is just that..engine oil. Its life cycle is limited due to its composition, operating temperatures and subjection to contamination(carbon). Hydraulic oil is specifically designed for transaxles that operate under such conditions as high temperatures, high pressure and basic extreme conditions that regulate how it is manufactured... specifications of its composition due to its designated use. Why then do I get this push-back from dealers that swear engine oil(SAE30) is ok for these units? I can think of only one reason they want SAE30 in these units...service money......year after year after year. Has anyone ever taken this battle on with your dealer....if so how did you resolve it? I don't know enough to swap my transaxle fluids out myself.....to risky...best left to those that do it daily. But if this is wrong, and I believe that it is how do ya win this arguement? ANYBODY....?