Have a dumb question, my apologies if already addressed. I have two jacks that just don't lift anymore. They'll rise until they contact the frame, then won't raise any more. (Yes, they have plenty of fluid in them.) My understanding is that these things are essentially bottle jacks mounted sideways in the frame. I know you can buy sets of rubber O-rings online to rebuild them. What am I missing? Seems like a fairly straightforward device - why are they crapping-out on me? Anybody here ever "rebuild" one? Is it worth the effort, or should I just haul them over to the scrap yard, and stop by Harbor Freight on the way back? Thanks for any advice!