Sorry for the delay updating.

I got the reels repacked, which was pretty easy. That got a lot of my drift taken care of, but I still have some. If I tilt up the heaviest pallet we have (~2500 lbs) it'll still drift down in a couple minutes.

To figure out where it's leaking, I tilted up a heavy pallet, then disconnected the hydraulic line that's pressurized for tilt-down (rod side of cylinder) right at the reel connection. While it drifted down, I saw no fluid exit this line but a couple of drips. So I'm thinking this tells me that there is no leaks in the reel or cylinder (again, no external leaks), which I'm thinking leaves me with the tilt valve itself.

Thinking that there might be some o-rings in there, I very carefully took the valve apart. I'm sure you already know it doesn't. Everything looked fine: I couldn't really see any real scores on the spools or the bores, however there were some marks. Defeated, I cleaned it carefully and reassembled it.

But I think it has to be the valve since the fluid has to be going somewhere, and it's not coming back down the unpressurized line. One thing I haven't done yet is to change the hydraulic fluid. Wishful thinking, but perhaps it's gotten thin? The plate calls for SAE #10, I've been using HF32. I assume that's correct for indoor use?