Description Reviews Supertech MINI Cooper Valve Seals! Regardless of your needs, Supertech provides the best solution for both performance and improved durability. A valve Seal keeps the oil out of your intake or exhaust path that will literally want to get sucked in while the motor is driving. Low oil situations only accelerate the problem and can cause other engine damage. ANYTIME you are removing the head you should replace these! Supertech valve stem seals are made from a high-quality rubber compound, which feature a special compound for high temperature use, and designed with a reduced outer diameter for optimum valve spring clearance. These valves seals fit a 6mm valve stem for all of the Gen 1 MINIs. The guide OD: 11mm/.435" and the seal OD: .551" / .670" bottom.