I took off the black cover and found the black rubber buffer in the lock, however, I think I have to replace it, since it is very hard to stick anything onto the rubber buffer. There is some grease in the lock, even you can stick something on it, it will not last long. I ordered the lock via BMW of Bloomfield, it costs 53 bucks including shipping.

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--2004 E53 X5 4.8is - ECE version; right hand drive; Located in Hong Kong; ext. black sapphire metallic; int. leather black; adaptive dynamic bi-xenon headlights; 16:9 onboard monitor w/o navigation; 20" genuine BMW Y-spoke 214 wheels with Bridgestone Dueler H/P Sport tires; Int. rear view mirror w/ compass.