do you have a leak in the oil ie constant relevel.do a relevel test on the bottom floor with the emergency lower on the block and see if it relevels(on auto).also how much overrun from bottom sill to springs is there? i wonder if the room is shollow and the relevel is to close. i way to check if the lift is left on the bottom floor and is slipping down is to shut of the lift o/night to test the hydrolics and at least you will know.if you have checked the bypass it certainly seems as tho the lift is bypassing but i wonder if the up valve is sticking as well.
