you can tap the hole that feeds oil to the cyl for a big grease fitting. then fill the cyl with gear oil thru the hole. put grease fitting in.. then pump some grease to it. pretty much has to come out.. that or pop the 4psi hose the grease gun has ( usually ).
ps. closed end of piston goes into bore. oring first.. backup washer on the back side. oil presses the oring into the backup washer and that into the ring land wall. BU washer protects oring from cutting
cup end of piston faces out for dogbone to ride in