You are incorrect. The 124.028 (ie your car) always starts from rest in 1st gear. That is normal and correct operation. Earlier model year 300Es had 2nd gear start, but by the time the M104 engine was introduced (in the USA) 1st gear start had been adopted.

I have one of these cars as well. The transmission shifts a bit firmly when cold, but shifts are very quick and smooth when fully warmed up. Of course this is all subjective; it depends on your definition of "firm", ambient temperature, synthetic vs. conventional ATF, etc.

If you have firm shifts the first thing is to find and fix any vacuum leaks on the engine or vacuum lines. Even surprisingly small leaks affect shift quality. The electronic engine management on this car is surprisingly good at adjusting to and hiding vacuum leaks, so you can't assume there are none just because the engine still idles smoothly at the correct RPM.

- JimY