squeaking chirping noise from front of engine

Greetings, I have been chasing an engine sqeal on this Taurus for months now, not much left to change but here goes.
Chirping or squeal started and I thought for sure it was the water pump since the car was leaking coolant. But no, turns out the coolant reservoir was cracked on the bottom.
The water pump is good, no leaks and the shaft/impeller have a good tight feel like a new one, so I reinstalled everything.
During this I noticed the power steering res is leaking, so I change it.
I spun the alternator while the belt was off and noticed a bit of a hushed chirp, so tired of this p,o,s and just install new alt, no dice, still squealing chirping, over the next few months I replace the serpentine belt 4 times, each time I replace the belt the noise stops for anywhere from a few hours to couple of weeks, but always comes back.
I spray just a bit of water on the belt and the noise stops for a short time.
Also replaced tensioner and idler pulleys both, cleaned every pulley spotless thinking the leaking power steering fluid contaminated the belt and pulleys.
Also used a small wire brush on both sides of the belt s with some degree of success, but that stopped the noise for only a bit, like an hour or two of run time or less.
No noise when run without the belt.
To recap; everything except the AC and water pump pully has been replaced, the noise comes from back toward the firewall.
Only thing in that area is the water pump pulley, I see nothing wrong with the puley, even under magnification. Really??, 50 bucks for a new ( plastic ) pulley from the parts store, and though I have used an automotive stethescope and rubber fuel line the noise is difficult to pinpoint. Obviously. I have had several different ears put to this thing in attempts to pinpoint, and each time they agree where I think the sound is coming from, yet, No.
I guess its pretty silly to ask opinions at this point being there isn't much left to try.
Water pump pulley, AC, this though I really doubt AC because the noise doesn't point to the front of the car.
I have never heard of a pulley going bad like this, but then this is the first plastic pulley I have ever dealt with, anyone else experience pulley problems from these cars??
Thanks for any input.

Sheesh, it does sound like you've covered the bulk of what I would suggest. One thing it doesn't sound like you've tried yet is to carefully wire brush the pulleys that are not new (crankshaft pulley, PS pulley, maybe an idler pulley, etc.) to makes sure there is no belt/grime residue in the grooves. I've read of others having belt noises that fought them which they eventually solved by wire brushing the pulleys.

Also, when you replaced the belt did you replace it with the same type of belt or have you tried different brands? Years ago, shortly after serpentine belts started becoming common, Goodyear Gatorback belts were the belt of choice when trying to quiet a car with a noisy belt.

-Rod