Gasket for dephaser cap - available?

Hi - I've finished my timing belt job and noticed what I think is a missing o-ring or gasket. I see what looks like a plastic ring on the old dephaser pulley but don't think I could or should try to save it.

Can this be replaced or is it new cap time..

I managed to remove the old washer thing from the old dephaser. I'm assuming that should be OK.

Reuse the old one, should be fine. Run it up and check it doesnt leak