It's normal for belts to look like they are vibrating. As for the grooves in the pulleys being worn, they won't pinch the belt. What happens is the sides of the belt wear causing the belt to sit deper in the groove which is ok until they get deep enough to touch the bottom of the groove. Once that happens, the belt will loose it's grip and slip. "V" belts work by gripping on the sides, not the bottom. As to tell if the pulleys are worn, you have spun them and felt no roughness, also check to see if you can grip them and make them wobble. That would indicate worn bearings. My guess is all is ok. The mower deck on my 316 was replaced about 20 years ago, and the bearings are still good. I replaced it because the first 6 years, I used it commercially, cutting about 12 acres or more a week. The deck shell itself was so beat up, it wasn't fixable.