heater pipe leaking

[VTPREDATOR]

on the top heater pipe that connects in behind the alternator is leakin. i tried to use a rubber o ring from repco, but it was too fat and it sliced itself when i tried to refit the pipe, hence still leaking. my question is what am i supposed to use for the correct fitment?

cheers,

[Fu Manchu]

get a whole new plastic pipe from holden. was cheap as. came with the correct seal.