Hey Bruce, I think I've given you enough to at least have you question your previous assertions. In my mind, the used tank pump combined with no specific test to find out if it is performing adds up to speculation about the origin of the screeching sound from your main pump.

The sound of cavitation in the main pump might be described as screeching. But I'm with you if you're thinking it has screeched long enough to give you the impression there's now slop in the armature bushings. There has to be a point after which a main pump is abused beyond recovery.

And when I replace it (despite the fact it is still not being fed by the tank pump) and find the replacement pump creates enough pull from a full tank compared with the older pump, I'll declare success, and begin the cycle again.

Bottom line, wait until you're down to less than a half tank, pull the input to the main pump and run the tank pump by itself (power to right side of fuse 5) and satisfy yourself that tank pump can deliver the fuel, before swapping the main pump. Volvo eventually "got wise" and stuck a Schrader tap on that line, but it was about 10 years after your car was built.
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Art Benstein near Baltimore

In democracy it's your vote that counts; in feudalism it's your count that votes.