While blind installation of new or old/crashed servos without a simple burn in for a short period on the grounds that you are wearing out the servo may be acceptable to some however that premise is about as absurd as saying the same for breaking in an engine.

The original question was "how to test old servos" and the fact remains that inaddition to feeling for stripped gears manually running the servo in a continuous mode for a short period with a servo driver is an important part of that "test".

John