Thanks guys!!
Can't remember which one it was, but an online review I was reading when researching the new truck mentioned that all update E53 were getting a 'soft tailgate'. It didn't really delve any further into the issue, but it made it sound like the auto open and close tailgate on the latest ML's and the like!!
I wasn't too concerned if they have them or not, but at least now I won't be trying to fix something I don't have!!
Haha.