Sorry to hear about the milk in your log splitter. Never a great thing.I'm also using the same 5-30 oil with the addition of Mobil1 at filter changing time. I have thought about a total hyd. oil change, just never got around to it. I guess with enough filter changes I don't have to worry about it.
On a somewhat related topic, I noticed some milky white fluid in my log splitter's hyd. oil...figured water. Changed out the oil and I still have it. I drained as much of the oil and used the mfg. recommended oil. Is another (or 2) fluid changes needed? Do I need to flush it somehow?