The biggest reasons I see for not using the drain plug on the late V6 and V8 is that the oil usually makes a mess. One of my techs showed me how to cut down an antifreeze jug into a funnel with a tall brim on one side that he jams into the suspension on MLs (my wifes car needed an oil change). Really worked good, not a drop on the car.
The FSS can be reset using the trip odometer. I don't do it that way so I can't explain the dance but it is explained in the owners manual.
Bosch Master, ASE Master, L1
33 years MB technician