Hey Mike, PITA.....the trouble is getting the residual air out of the lines near the cylinders. No matter how hard you try there will always be a little air in the cylinders that comes out with repeated cycling and in long runs it will just snorkel up and down the lines from the cylinders. I will install a T fitting nearby to bleed off that air but the whole process is very messy. Air all the way unless you absolutely have to go oil IMO.