Gasket material

[Chainlube]

Theres 2 little metal rings on the piston, I broke one of them trying to slide it in to the cylinder. Had to try and pinch them to close a bit to squeeze the piston in the cylinder. Broke one in the process.

Oops! Someone should have mentioned to check the end play of the rings before putting the jug back on.
To do that, you place the ring by itself inside the cylinder. Then run a feeler gauge between the ends.