TT2
My comment was more around the principle of "There is a fault (allegedly) therefore you must change something" backed up with the problem of not having the spares you need.
Therefore you change something that you do have a spare of in the hope that it makes the fault go away, although how many "faults" end up being unrepeatable was always a cause for concern.
But I agree the level of diagnostic engineering appears to be on the wane. It was so much easier with valves, you just looked for the cold ones.....