Well.. definately old or bad wiring could definately be a culprit. How old are your cables, and how tight are you tightening that ground wire to the starter? I've had mine not start before, and act like I had a dead battery because something was a little loose. A little loose, means more resistance, which means more heat, and heat kills all things electrical. If you are in doubt about the wire, put a multimeter on it, and check the resistance of your wires. Should be reallllllllllllllly close to 0, if its not, you just found your problem.
Also.. as far as reman units from AZ, or Advance... they only fix what is broke, not rebuild the whole thing. If the spring was sticking, they'll replace the spring, say the brushes are about 1/2 gone... that might be good enough for them. I had a problem with AZ starters on my truck, and finally after the 3rd one, I got it rebuilt by a local guy. haven't had a problem with it yet.