"shut off while driving".

I had this happen about 10 yrs. ago with my 91 300-SEL. Has the same engine as yours.

My MB would simply die after driving about 8-10 miles and in warm weather only. I'd pull over. let things cool off; then restart and run another 8-10 miles and it would die again while driving. If a cool front blew thru and temps got down in the 50s-60s or lower, the car would not die, but once it got up in the 80s the car would die after 8-10 miles of driving.

Turned out to be a bad fuel pump.

Interestingly enough I also had an engine dying issue that was solved by jumpering pins 1 & 2 in the MAS relay. That gadget sells for $399 on ebay and it's rebuilt. The OVP - overvoltage protection relay has been accused of causing similar issues. It's around $50.

I was unable to find a MAS relay at this forums parts section? Leads me to believe that these "rebuilt" MAS relays are junk. PeachParts apparently stopped selling them.