The Autozone, O'reilly and Napa alternators and starters are a 50/50 proposition; either they are good or bad. Never buy the "economy grade" parts that have either the 90day to 1 year warranty, the repair quality borders on slip shod, its greatly improved on the "premium" lines. Though they don't like to do it, have them test the replacement unit you are buying out of the box... It will be either good or bad and sometimes you can even hear the bearing going bad over the motor noise of the tester. Local rebuilders are almost always better, but more costly than chain store replacement units... chain store units are repaired mainly in Mexico where labour is less, shipping is the main cost in many cases. Local labour in the San Francisco area is about $75 for electrical service... so repairing your unit is usually far more expensive.