lifters fail by either locking up or having too much slop. I wish there was a way to test the strength of the spring because even if everything is freed up and moving, the springs could LOOK normal but be worn out and you could still get a lifter tick. If I was doing a lifter job, and the lifters had "high" miles on them, I would swap them out for new ones just based on metal fatigue of the springs. Your post could come in very handy on a newer lifter that looks good but is obviously frozen.