Your biggest problem is allowing AAmco to work on your Mercedes.
If you have a Ford, Chevy or Dodge and trans fails, sure, take it to AA(beep,beep)MCO. If you have a Merceds, you should have taken it to a quality dealer or independent.
That said, it is not normal and all of the flushing and changing of fluid in the world will not solve the problem. The problem is internal.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS