Sal, Autozone won't help you now that the part is no longer sold by them. Maybe they would offer a refund of your purchase price. However, the repair you need is pretty straight forward - replacing the accumulator.
Brakes seem to work fine, but, if the brake idiot light comes on for a couple of seconds, then goes off, the diaphragm in the accumulator ball is leaking pressure which causes the pump to run briefly to build up pressure again.
check out this link
http://www.gnttype.org/techarea/brakes/brakespage.html
Under brake maintenance, scroll down to "fix your powermaster part 1" and review the "accumulator operation" chart.
to replace the accumulator....
ignition key off, depress brake pedal firmly at least 10 times to depressurize system. place rag under accumulator ball and cover fender and surrounding area (brake fluid will discolor paint). remove accumulator and old o-ring. hold accumulator with threaded end upwards so as to not drip brake fluid - it is half full of fluid. A drop will discolor paint if not removed in a few seconds. maybe have some water on hand just in case a drop of brake fluid goes awry. Nothing will spray out when the system is de-pressurized. Maybe less than a teaspoon of fluid will dribble onto that rag. Install new accumulator and o-ring, torque to 15-20 ft-lbs.
Accompanying service manual pages and diagnostic flow chart are attached.
If you have not done so, now would be a good time to flush the old brake fluid before changing the accumulator. there are many "how to guides"...maybe just use a turkey baster to remove fluid from reservoir and wipe out dirt from reservoir. Add new fluid and vacuum pump bleed - right rear, left rear, right front left front.
If the bleed screws on wheel cylinders/calipers are possibly rust frozen and you don't want to mess with them, at least change the fluid in the reservoir. that will get new fluid into the accumulator.
Kirban's sells a replacement accumulator
Cardone accumulator part# 6697
There are also plenty listed on ebay by various vendors.
And there are probably some used-tested -good accumulators available from other turbobuick members.
REMEMBER: it is brake fluid that deteriorates the diaphragm inside the accumulator separating the brake fluid from the nitrogen charge on the other side. So, in another 10 to 15 years, the accumulator will probably need to be replaced again as a service part. Also, maybe the reason you don't want to buy a used accumulator unless the seller can note what the current accumulator pre-charge pressure is compared to new.
