Much depends on which type it is and how it is oriented. Some are cast stainless, some are welded stainless. If the welded type is oriented where it can hold water in the jacket on shutdown, they corrode internally and cause big issues. If aimed where they drain on shutdown, they can last the life of the engine. The cast ones are better, but rarer. Lots of custom ones made by others than Cummins, those could be anything.
Post a photo of the mixer installed. And maybe a few more showing general layout of exhaust piping in engine room.
If you take it off, take a photo of inside of turbine exit.
Operator's manual I think has torque table for std metric bolts. Probably around 18ftlb for M8.
