I know Kirk (RIOT) has a Phantom Grip on his SRT, but I haven't seen him post in a while...he must be busy drag racing his boat.

Jake (lougn14) from Eurocharged has some experience with Quaife LSDs'. They are helical ATBs'. That would be another option, though I'm not sure of the applications for SLKs', but I've seen it on a couple Es'

EDIT: Just checked Quaife's website. Looks like the applications for Mercedes are only C32s' and E55s'... looks like you will have to stick with Phantom Grip.