Just like Ford dealerships, not all MB dealers will deal with a motorhome.
Regarding the oil change, the Sprinter requires oil that meets certain specs. DO NOT let anyone tell you it's OK to use an oil that doesn't meet these specs. A quick lube place can be a danger to a Sprinter. The oil filter is not a spin on canister type and if installed wrong, the engine can be destroyed. The filter is super easy to change IF YOU KNOW WHAT YOU'RE DOING. Alas, many of these oil change places do not. When I was working on cars at a VW/Porsche/Audi shop we saw more than a few quick lube place screw ups.