Chronic problem with the BMW. I have a code reader and the check engine light occasionally comes on due to the same small leak problem. If you go to MITCHELL ON DEMAND, you will see that this has been an ongoing problem. I too replaced the gas cap, and the light stayed out for months. Now, I dab a wad of petroleum jelly on the gas cap seal. So whatever pressure is leaking out of the spring in the gas cap most likely will not get past the petroleum jelly on the seal. The jelly should be re-added from time to time.