The modulator is on the side of the transmission (drivers side forward).
I recently wrote a lengthy description of the multiple adjustments on a 300SD. The situation is similar for the 190D. I wouldn't suggest playing with anything other than the modulator (it has distinct positions so it can easily be reset to original. The other adjustments can't be as easily retraced.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician