They still fail but its often because the mechanical DEF level “float” is fouled and that is eaily and inexpensively repairable. Also a bad DEF pump will mimic a bad DEF head. That’s why I’d like to see the codes and hear a bit more about this. Many people have spent a lot of money unnecessarily because of a mis-diagnosis and/or unscrupulous shops taking advantage of unknowing customers and covering up their own mistakes at the owner’s expense.
It’s also entirely possible that the DEF head is bad and Spartan has had more trouble with this problem than Freightliner as they used a different (worse) supplier for their DEF heads. I’ve had my share of emissions problems and I try to learn from every case I read about.
My 2016 coach is on a chassis built in 2015 so it also has pre-2016 emissions, and it has had the DEF head and DEF pump replaced, fortunately while the emissions warranty was still in effect. But the DEF head may not have needed replacement (I’ll never know) and the DEF pump failure (which the shop initially diagnosed as a bad DEF head) might have been avoidable if I had known then what I know now about these systems.