Yep.Cool job, thanks for the detective work. That makes more sense than wondering if the springs wear out.
So age and poor oil quality are the biggest factors to the tensioners going bad. Use best oil always, change more often, and replace the air cleaner often to. If the oil gets black quickly, check your air filter. That's either from dirt going through it, or a fairly worn engine.
Interesting, makes me wonder if high mileage oil w/seal-conditioners would help.