To me, the final nagging issue when considering a basic checkout, and replacement of the obvious issues that reveals, is what about other deeper, internal mechanical components?
For instance, if the PSG is found to be bad - and replaced, the pump MIGHT check out on the stand - but still have the expected wear and shortened lifespan in other parts resulting from however many miles might be on the pump at time of inspection.
I would guess that replacing ONLY a bad PSG for instance, could run the total close to $500 - but what about the remaining internal parts that might LOOK ok on a test stand - but not be actually taken apart for specific inspection?
Is it dollar wise to replace ONLY the obviously failed parts - and continue to run on the rest of the used internals - or better to bite the bullet and go for the total rebuild?
I still haven't figured that one out - and I suspect that is a question that the customer must decide on his own!