I'm pretty sure it has to begin with 124032. It might not be a continuous string. It might be more like 124 032 12 xxxxxx. The chassis number will also be on the body, but I don't know where on a W124. On a W140, it's under the mat ahead of the front passenger seat. I'm not sure where it is on either of my W126s.

Sixto
91 300SE
81 300SD