Never had mine apart, but similar one on a MF14 just had O-ring for main seal. The wiper is just that...does not hold the pressure back. The big plug cap where pin goes through comes out. Hard to do, but it will come out. Take the fitting off next to it, then use a tool to push the plug out. Once out, the piston/rod will simply slide out. Then the seal/o-ring can be replaced easily. The o-rings aren't std. I had to go to General Rubber & Plastics to find that size. Note: that seal cap "may" come off also, but I'm not sure about that. I am sure about method I described above.