Hi all I recently bought a new rad cap for the 4A, Moss part no GRC112SS which has the lower siphon valve for coolant recovery systems, however this cap no longer comes with a rubber top seal under the cap a relies on the spring steel disc to make the seal. PHOTO 1. A friend also bought a cap for his TR6 at Stratford upon Avon Interclub and it didn't have a top seal either.
Question is will the cap with just the spring top seal and no rubber top seal be airtight for the coolant recovery system ( I doubt it). I have at the mome