My car is a 124. I also had a problem with my fuel gauge, specially when the tank was less than 1/2 full. I replaced the fuel sending unit and my problem was gone.
Is this the same problem that you have?. May be or may not be. Every car is different!.
However, for what I read in this forum, it is very common. Probably you already did a search, so you know how many posting there are on this topic. Come out with your own conclusions.
The only way to find 100% sure answer (maybe) is to take it to a trusted MB mechanic and have it fix it.