Description Reviews MINI Cooper S Expansion Tank Cap! These fail from time to time on R52 or R53 MINI Cooper S's. MINI updated the cap on the inside and the seal a while ago. You can tell by the bright blue seal inside of it. This is a brand new OEM design. Comes with a 2 year unlimited miles warranty from MINI! This great addition to the Forge tank, since the tank doesn't come with a cap!