Mass air flow Again? 97 f150

[Cessnadriver]

About 3 weeks ago, I cleaned my mass air flow sensor on my 97 f150/4.6.
Problem was missing/hesitation on acceleration. Cleaning it VERY gently with alchohol and a Q-tip seemed to help it quite a bit.
So, I tried removing it and spraying it with electrical contact cleaner, as recommended here. Almost right away, it seemed to run worse. I wrote it off to adaptive measure on the part of the OBDII system. However three weeks later it is no better, and is getting getting worse, and the mileage, which I've been recording since November, has dropped from 16mpg to just over 14mpg, in town/commuting. My question, what are the symptoms when these sensors finally fail for good? Are the "rebuilt" ones from NAPA as good as the dealer item$$? just looking for someone with some experience in this area.
Thanks