There were manual 5-spds hooked 4.5/5.0/5.6 motors but not from MB directly. AMG had these as an option if you wanted it, was a Getrag 5 sp 'box. The factory did not have a 'box strong enough and even used their auto 'box in there rally cars as it was the only thing in house to hold up to the stresses.

Dave
'85 500SEC w/ 187k miles - daily thrasher mobil
'87 560SEC AMG Widebody w/ 51kmiles (but alas an autobox...)