Don, there's a fairly cheap way to stabilize the tilt cylinder. If you use quick-connects at your remote valve, just disconnect the hoses. If it still leaks down due to the hoses expanding, put quick-connects directly on the cylinder.
Center the cylinder before disconnecting and reconnect after you finish. (Don't connect or disconnect with the weight of the mower on the 3PH because the fluid will be under pressure and you may not be able to get the connectors loose.)If it drifts with the quick-connects disconnected, the cylinder is leaking internally and a piloted checkvalve won't help that.
Of course, if you wanted to adjust the tilt for any reason while mowing, this won't work, but I rarely need to adjust tilt. I do sometimes adjust the toplink when cutting over the side of a gully or a pond.
