MB should have made the 300SEL first gear start. It NEEDS it.
When you want to take off briskly, shift down to '2' then back to 'D'. This will start the car out in first gear. This is really useful if you have to cross two lanes of traffic with no middle lane.
Otherwise take off from the suicidal 2nd gear and give the car a quick half-pedal throttle. The transmission senses the urgency in your actions, and drops to first automatically. At least mine does. You do not have to floor it.
1987 300SDL (324000)
1986 Porsche 951 (944 Turbo) (166000)
1978 Porsche 924 (99000)
1996 Nissan Pathfinder R50 (201000)