Your friend may be on to something. I know that I typically raise mine to get across the threshold of the shed, but when I come back a week later the deck (and the right front tire) is down.
Maybe raising a deck and leaving it is like raising a vehicle with a hydraulic jack and leaving it there. I know the manufacturer of the jack recommends storing it with the valve backed off 1/2 turn and the pressure released.
Perhaps a hydraulic jack and a hydraulic lift are different, I can't see how, but perhaps they are.
