I do not know exactly what system Mercedes uses.
If it is similar to the 70s Saab 99/900; then a charcoal canister is part of the evaporative emission control system. The charcoal is a temp storage device for gas tank fumes; after a period of time the coals become saturated and must be changed.
With the Saab, I opened up the container(it was not meant to be opened, slows me down a little), dumped the old stuff and renewed using charcoal from a per store (Hertz ? brand).. cost about one dollar.
Why did I not use charcoal briquettes ?? Good question..
I was looking for a source of charcoal where the cost was 25 cents per pound or less..
My philosophy is if something, anything can be completely fixed for "pennies", then go for it.. My labor is free now; when it was not, it was still the thing to do.A little work never hurt anyone.
'80 Mercedes 300D ..sold..
two Diesel VW caddies, old ones ..sold..
'96 Saab 900S