[rohrmann]

No where have I ever read in any Lippert document that says ATF and conventional hydraulic fluid can not be mixed. ATF is hydraulic fluid, just has some other additives for use in a transmission. I drained the fluid a number of years ago and filled with ATF and CAT stiction fluid, and the system still works just fine. I would not worry about mixing, just make sure you use good fluids as recommended by Lippert and your system will be fine.