re sealed a tilt cylinder today on a nissan (well i thought i had) but the mast keeps creeping forward.

removed the cylinder and checked the seals and the packing rings (nylon- solid) that go either side of the o- ring looked a bit ropey.

how do you fit them without damaging them? i tried heating the new one's up in boiling water and still there a pig to fit. is there a tool needed?
they are very brittle and dont take kindly to screwdrivers.