there are common problems with the 600 series failing i.e the 645 and 625 but some people i know have had them servos in his bug for over a year now with no problems

my 645 an 625 failed[&o] a good servo to buy is the ACE DS1013 very durable no problems with them, waterproof,dustproof 13k of torque and at 10secs one hell of a servo
also another great servo is the sanwa erg-rz