Hi, just thought I'd poke my nose in a little. I have an International 3400 backhoe that drove me crazy for a long time with foamy hydraulic oil, and cavitation. A diesel mechanic friend of mine finally came over and we trouble shot one day. When I would rev up the engine, the hydraulic pump would begin to cavitate, but would slowly stop making noise . As it turned out , air was being sucked in thru an o-ring and it was just luck that we found it. After this experience, I 'd go over any and all connection that you have--replace any o-rings--make sure everything is air tight. My mechanic friend told me water in hydraulic fluid turns it a milky white, depending upon how much water you have in the system. Foam is air in the oil. Hope that helps.