Aussie, yes, I have done just that, and it is a very standard seal. If I were at the boat I could give you the part number, but I am not...
So, what I did was to pry out the old one, and even though it was badly distorted in the process the seal shop was able to work out the replacement, and installation
is simply tapping it back into the recess in the plastic bit.
Buy a couple of extras while you are there... they are less than two bucks each IIRC.
Easy peasy, mate, so good luck and no squirts!