Coolant Expansion Jug Cap

Is there a gasket in the Coolant Jug Cap? When I changed my coolant temp sensor, I discovered that my coolant system would not hold vacuum. Checked cap and found that there is no gasket to seal the system. I would think there should be a gasket there.

Bump - any answers out there on this??? If I could only find that VW parts link!

The only seal on mine is the o ring that goes around the outside of the center blue thing... I can snap a pic if you like.

-Jason