The factory single-clutch automatic is the one component owners commonly criticize; one commenter argues the car would already be a $250k car if not for the gearbox. The near-universal recommendation for anyone who drives the car is a Renntech Speedshift rev-match/throttle-blip TCU tune, which now requires the valve-body upgrade; Weistec reportedly no longer offers the TCU tune.
The automatic transmission and the rev-match TCU upgrade
Mercedes-Benz CLK63 AMG Black Series (C209) · driving