The S6 method is a bad idea in my opinion.
The issue is in the SAC (self adjusting clutch plate) and the SMG adaptation. Overtime the SAC adjustment becomes out of sync with the SMG adaptation hence the slip you experience.
My experience with this is a simple clutch slip point recalculation under the GT1 which will usually solve it.
If it's really bad, then reset the longitudinal acceleration sensor also ... and always remember to reset the clutch curve
