I have been given a hydraulic jack that does not seem to pump. There is plenty of oil in it, or was as I have stripped it down to the bare bones as it must have been used in a field as it was caked in muck. Anyway, as luck would have it it is the same as a one I bought, (second hand then) in 1978 and have still got and it still works. What I would like to know is what the two hexagon headed bolts on top are hiding and what fluid would be best to use to flush the jack out as there seems to be a fair bit of muck still in it. I took the pump rod out, no seals on that, and the ram came out and seems to have a hard seal and looks good. No leaks from that anyway. The release plunger has a tiny o ring on it. The pump casing is a one piece lump with the ram casing welded to it so it cannot be taken down more than removing the bits I have and have yet to when I know what is behind the heads. The last photo is another old jack I have got and would like to know the make of it as well as the one I am working on.