i'm a proud owner of a 2005 cooper s convertible, and new to website. i bought the car a few months back, so far, no issues until yesterday. lost coolant and overheated. refilled the resevior, and ran it until operating temperature. coolant is now "oozing" from under the coolant resevior cap. so....bad cap seal or bad thermostat that wont open? any ideas? thank you in advance.