The real dig is the software. Even if you manage to change out a defective uP, chances are high that you will never have access to the software that goes into it.
I designed the boards and wrote the firmware for boards where I had to do the work. I had a subcontractor build the boards, so no need for fancy tools. Over a 5 year time frame, the only hardware failures were one electrolytic cap and one temperature sensor with lightning damage. It was a pretty high G environment on a coal carrying railcar.