Description Reviews MINI Cooper Non Return Valve is a small item in the head that keeps oil headed in the correct direction and from draining back out of the head. It's under the Vanos Solenid depending on model. This part can strip out coming out when rebuilding the head and should be cleaned out of oil buildup to make sure the flow of oil is good after a rebuild. The N14 & N18 Cooper S only have (1) each, and the N12 & N16 Cooper have (2) each.