The Fuel sending units are accessable..With the car on a Lift
There are Plastic covers on Each Side of the Tank That Will Expose the Fuel level sending units...MB Makes a Factory tool to remove the Metal Ring that secures the sending unit to the tank
But You can Remove them without the tool...Just takes Longer
Also Please Make sure that The Fuel tank is Drained BEFORE you try to remove the fuel level sendings.....
I Have Done Several Of the Sending Units on Most all Late MBs