Thanks for the reply.

You may be right about the reason why this is happening.
So, I wrote this comment back to Mercedes, because I have also spoken to
other customers here and they also consider it as a known "standard"
Mercedes problem.
Time that Mercedes quality control is going to do something about it.
I told Mercedes customer support my next Mercedes will have to come with an
extra guarantee for the seat.
I would suggest that everybody would put this request in the contract when
buying a new Mercedes.
This would certainly help to get things moving for a better quality future.
All the best
Sylvain