Hi torino. As you said the main piston is not going to be the cause of the washer going down slowly. If it is broken at the edges or has a damaged bucket where it will affect most is that you will have to leverage more times but it may lift some weight. You also have to replace them so that it works well for you. You can search the houses of spare parts for brakes with the measures used. The problem is in the anti-return valve, this valve is what keeps the lift in position until you release the lever to lower it. You have to take that piece apart and check that it has to be chopped or broken. As for the oil you can use ATF fluid but personally I prefer to use 15w40 is heavier and does not leak as fast as the atf. Below I leave the scheme of a hydraulic jack that is the same principle that the lizard types use, where it says "one way valve" is the anti-return. I hope the data

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