To close this one off, I ended up buying 3 different O rings for each size with various cross sections, and fitted the ones that I could only just squeeze in, the drip has now gone.
Good job ! How safe and sturdy does the lift feels ? Also how much it was ? I need something similar for my garage but i am in two minds if to get the maxx jack's type with two independent low ceiling height columns or a scissor type lift- i need a 3,5 T load ratting as i want to cut a small pit there as well ! As much as i hate pits, i need room when dropping gearboxes and stuff like that ! Nice setup you have there mate !