From the 2012 F350 diesel supplement owners manual.
"Importance of maintaining the DEF level
In order for the SCR system to operate properly, the DEF level must be
maintained. Generally, the DEF tank should be filled during the oil
change service interval. See the scheduled maintenance information in
this supplement for more information."
I would expect a dealer to follow the guidelines in their factory manual.
At the time, while I doubted the tank would take 10 gallons, I really wasn't sure what the tank size was. And I was done arguing with them.
