If you take off the stop lever you'll find on the shaft an o-ring that's probably seen better days. MB doesn't list such an o-ring and I couldn't match the o-ring at Pep Boys or Autozone but generic o-ring set had a pair that more or less bulked up to the size of the original one. It's been holding for 2-3K miles now.

The stop lever comes off more or less the same way the shift lever comes off the shaft through the neutral start switch. In other words, remove the bolt that holds the stop lever in place where the shaft necks down.

Sixto
95 S420
87 300SDL