I am posting this thread in the hopes that it saves someone the apparent wild goose chase of finding an off-the-shelf o-ring that properly fits this application?

I had to replace the coolant flange on the rear of my 3.0L... which required disconnecting both the supply and return heater hoses. Reusing the old o-rings was a bust (leaked under pressure). So I tried matching up the rings at the local auto part stores: no luck... the correct diameter ring was always too thin. I then tried ordering several different sizes online... also no luck.

The catalog for this application specifies that the whole heater hose must be replaced since the quick-connect couplers are crimped on the hose (expensive and annoying). Others had mentioned the replacement VW quick connect part as a suggestion but I could not find a definitive confirmation that it fit and the VW catalogs only listed other applications.

If you have this leaky hose problem... do yourself a favor and pick up a URO 3B0122291B ($3.99 from a-zone... they'll have it in one day after ordering). Pop the o-ring out of this connector and marvel at the fact that it's a perfect fit. The $8 you'll pay is nothing compared to the aggravation of getting to these hoses again in the future.