The body control module is located behind the glove box on an E53, and no they are not all the same! You need to get it on a diagnostic before you start changing modules and preferably a proper BMW system, all E53 operate a k-bus system and your about to entre something you may wish you never started, a basic diagnostic system may throw up a body control fault but a BCM does a llooooot of stuff and that is where the fault may lie (ie a bad earth) somewhere further down the line. My advice is to find the BCM and check for water ingress, if that looks ok empty the boot and root around in the wheel well for water ingress if that's ok unless you are very talented leave the fooooook alone and get a pro in. Regards Steve