When I was learning to fly R22s in Australia, the three items pointed out as potential damage indicators were 1) dinks in the fairing below the pylon, 2) wrinkling on the underside of the tailboom at the forward end, and 3) the "smiliness" of the rear lower crosstube.
Anything different / odd about those three mean I need to talk to someone.
And the swashplate gaiter is an item which should be checked every day as part of the Check A / daily / whatever.