Hi I have a Weistec stage 2 supercharged SL63. I have had it on for about 6 years and about 30,000kms. Love the power. The only issue I had was that I just recently had to replace 3 pulleys, one started to deteriorate and that cut into the belt and pulled the other pulleys out of alignment and they were on verge of similarly failing with bearings shot. 30000 kms is not really a lot in the scheme of things but it was a cheap fix AUD600 or about US$450. I guess I am lucky I didn't get an issue whilst doing 120/hr in some twisties.
car is a beast and never had a trans issue whatsoever