I did see a website where some company was offering rear-end swaps for Mercedes.
Of course I can't find it again!!! I thought I had put it in my favorites! Guess not!

Anyway, they didn't have one listed specifically for the SLK320, but they did have a general price range of several thousand dollars!
(Because the gears in MB diffs are hand fitted matched gear sets)

I'll keep looking to see if I can re-find that site...
Matt