Hi
I had teh same problem with my clk 430............first the new senders must be the UPDATE version because MB knows that this items had problems.
Aftrer change the senders disconnect the batterzy for 10 minutes and after drive the car normally untill the 1st tank is gona.
After the clustre will show us the exact level i do not know exactly but it is like auto calibration...
On my car this procedure worked.
I jope this help you
Alberto