That sounds just like the fuel water separating filter we still have on our boat. It is a PITA to seal it properly after replacing the filter element so we are replacing it with an all metal new Racor unit (~$100). We have a gas engine (A4) so the plastic filter is kind of a no-no when installed in the engine compartment.
I'm not positive that this filter is the right one but it sure looks like it: Racor Filter 2020PM-OR Filter Element
IIRC, these filters were not particularly expensive (around $15 a piece) compared to the new unit which has the filter enclosed in a metal canister.
The last time I bought filter elements for this unit I got a few extra. I know I have at least 1 unused filter element I could send you if you are not in a big hurry. I could send it/them off within a week. You pay postage.
PM me if interested.