Genuine Audi - HVAC Heater Core Seal Gasket - TT Mk1Your vehicles heater core handles hot water from your engines cooling system and transfers the heat to the cabin in the form of comforting heat from your vents. A failed heater core can leak that waterwhich is also called coolant or antifreezeonto the floor on the passenger side. If your Mk1 Audi TT needs to have the heater core seal gasket replaced, it's a job best left using genuine Audi parts.