Only Cub Cadets - 128 sudden vibration

I decided to grind up a few leaves this afternoon with the 128. Turned out to be more than I first thought, ran out of gas. Engine stopped real quick. didn't think anything about it, went and got gas, fired back up 10 minutes later. When I cranked back up, it was a little slower to crank than it seemed it should have been--almost cranked up flooded as it belched a bunch of black smoke--also had a bit of shaking goin on. Anyway, cleared out after a few seconds and back to work I went--no I didn't bother to investigate the shaking, figured it was all result of running out of fuel/restarting. When I stopped mowing and slowed the engine down, I could feel a fairly strong vibration. Blew off the debris from the leaves and did a quick inspection of the driveline. Clutch has wear on the 3 holes but doesn't appear to be broken, pins in driver, clutch functions OK, free travel seems like it has been for the last 20 years. Since I was done mowing, I didn't check the PTO--didn't feel like playing around the hot muffler. Anybody care to take a SWAG at what's causing the vibration? My guess is either the driveline or PTO didn't like the sudden stop. It'll probably be at least a week before I can get it to the shop, just looking for potential problems ahead of time.