The mast cylinders drift about 12 inches in 10 seconds EXCEPT when there is a significant load (1000 lbs +). Under load there is virtually no drift. I have had lift "mechanics" (I say that because they do PM work primarily so don't know how to troubleshoot hydraulics) look at it but I can't find one who can say what would cause drift except when under load. One guy capped the left cylinder and no change then capped the right one and the drift stopped. Is there something in the cylinder that would allow bypass but not when under load? Thanks for any help.