Helpful Hints for changing the oil...

Frequently, the canister cover will be very difficult to break free. Use a breaker bar with CAUTION! You may need a 'low profile' socket due to the limited space available.
If you loosen the filter canister cover enough to break the seal, it will help drain the oil from the filter as you drain the oil pan. Less mess later!
When replacing the O-ring, save the old one just in case (will explain later).
When replacing the O-ring on the canister cover, make sure you lubricate the O-ring with PLENTY of fresh oil before you install it, and lubricate again after it is in place. If you fail to do this, the O-ring will bunch up and cause a leak! (Click on the following link for the complete article.) http://new.minimania.com/Mini_Cooper...-53_Cooper___S