I don't know that much about servos. I started learning (not much progress) to fly a Blade CP Helicopter about 2 years ago. Got 4 servos out of an old crashed Aero-sport 60, hence my need for the servo tester, which worked great. You will get the grinding sound when you attempt to move the arm past the stops The servos I tested were weathered and dirty, but turned out to be fine. Haven't worked out an AVR assembler routine to run them yet, but have a couple of projects in mind.
Anyway, the tester I posted the link to works good, the parts don't have to be exact, the caps and pot I used were close, but within a few standard values...