Describe in detail, symptoms?
have you checked the fluid level?
My guess probably not because it doesn’t have a factory installed transmission dipstick.
Check tranny fluid level is the first item to check.
Box truck operating continuously transporting heavy loads in city stop and go traffic? Are you or employees heavy or easy on the foot feed? Employees are notoriously well-known abusers of employer vehicles. Just observe, among others, taxis, FedEx and UPS drivers.
When was the last time tranny fluid changed?
Service intervals are recommendations, and must be adjusted according to vehicle operating conditions.
Driving habits and practices, particularly heavy acceleration contributes to what Mercedes describes as “arduous” driving conditions.
Finally, don’t believe everything a dealership says, get a second opinion.