Inspected doser injector and scr can because def hose was leaking and found this inside scr can..... always inspect and take extra step to inspect inside..... probably going to be checking inside scr every yr as maintenance schedule.
Yes DEF fluid can and will build up in the decomp tube and cause problems
Im not sure on cummins
But on Detroit you can unplug the def doser and do a regen and it will clear it
volvo (im new to) you have to have vcads and do a B regen (basically it regens without turning on the def doser) to clear the system of build up