This has been a long and winding road but I think I finally got to the bottom of it.
I got tricked into thinking that if the coach was drifting out of level, it has to be the jacks or the valves to them. I checked those out and ended up changing a couple of valves that were questionable and the drifting improved but did not go completely away. Then I noticed it only happens when the slides are out. I verified the Hydac valve to the slides was good. I then pulled all the slides in and then closed all the needle valves to the slides except one and moved the slide all the way out. I did it for each slide, one by one, waiting a day or two in between. The level only drifted if I had the bunkhouse slide out with only that needle valve open. I'm guessing I've got some internal leak by in the bunkhouse slide cylinder (I'm not losing fluid so no external leaks). I am going to try the fork oil additive to see if that helps. If not I'll have to decide if it's worth the trouble to drop the chloroplast and replace it. Wouldn't you know the bunkhouse was the last one I tested. When I opened the needle valve after closing the other two, the slide moved a little so I suspected that would be it.