Insite Help exhaust (SCR/DEF) service required

[Longshot]

Thanks all who provided recommendations on how to tackle this Exhaust SRC DEF issue.
Here is an update:
We dropped the drive shaft to get access to the DEF Doser Valve / Injector.
The 3 - 6mm bolts that hold the doser valve to the Decomposition Reactor all broke off even after applying generous amounts of liquid wrench and heat from a torch.
We pulled the Decomposition Reactor tube and drilled, tapped and helicoiled the DEF valve injector mounting plate and reinstalled the Decomposition Reactor.
We then tested the existing doser valve after thoroughly cleaning it - it failed the test and rather than any DEF coming out of the injector, DEF began to leak out of the DEF tubing connection to the valve. We replace the valve, gaskets, bolts and reassembled tubing and drive shaft. We then cleared the codes and went for a test drive and all is well.
But we also know that it is inevitable that another issue will crop up any day.

As most on this site have mentioned having Insite and Inline is an invaluable tool in diagnosing and resolving issues.

Best Wishes and Happy Holidays.