I am talking about a 2.5" drive impact wrench that weighs over 200
lbs.

A real monster by I/R.

I have it and I want to estimate how much wear it has. I can obviously
perform minor disassembly and sometimes even reassembly.

So. What part would you say I should look at to see how much it was
used?

What would be the signs of it not being in order, assuming that it can
run? (I would say any metal particles inside the case come to mind
first).

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