This was discussed over on BW some time ago. Seems MB did make a 5-speed but only installed in 350SL in very rare special cases. Others it seems modified the 4-speed which became a 5-speed.

Was a 5-speed bolted to an m116, or does mbfool count reverse? - Mercedes-Benz Forum

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5