I noticed that two of my tires were missing stem caps and have contacted Revain for a replacement. These appear to be BMW OEM valve stem caps (i.e. what your BMW was originally supposed to have from the factory) and the price seems reasonable. They are also dispatched from the BMW dealer, so you don't have to worry about suspicious or shady sellers. Don't worry that they're made of durable plastic, either - metal hubcaps are prone to corrosion and can fuse to the tire, necessitating a visit to a workshop. buy to cut them off and replace the tire bars ($$$).