IMO the wavy pattern on the bottom of the print is due to too much extrusion for the gap you've set up. The result is material being squished and squeezed all over the place. It's got to go somewhere. Subsequent passes are affected by the line already in place beside it, so patterns start to develop.

Regarding the failed small gears, I agree with beerdart on checking the hobbed bolt. You need to at least rule it out. With the motor mechanically out of the picture, make sure the large gear and hobbed bolt can rotate fairly easily. Don't tighten the small gear onto the motor and then install the motor; leave the gear loose on the shaft and mount the motor about where you think it should go. After the motor is tightened, *then* tighten the set screw on the gear. The goal here is to let the small gear position itself on the motor shaft. If you don't you could be forcing a lot of strain onto the gears as the herringbone teeth pull themselves into what seems like an alignment, but really isn't. And then see how the large gear rotates by hand. You'll feel cogging from the extruder motor now, but the rotation should still have a consistent feel to it. If it seems to catch at places, well, there you go. Something's wrong with the gear mesh.

What material are the gears printed with? I of course can't speak to your small gears, but I've seen some really poorly printed ones. If these are PLA, the small gear requires print thermal management or the teeth are likely not going to be shaped properly. One recommendation I've had for people is to watch the small gear printing. If you see the gear shifting around as the nozzle moves, the print isn't cooling off enough between layers and you're basically trying to print onto the equivalent of soft rubber.

If you have both the large gear and small gear loose, play with them on the bench and see if the herringbone teeth mesh smoothly. If they don't feel smooth on the bench, they won't be smooth on the printer.

Have you monitored the temperature of the extruder motor? If it gets too hot, heat will conduct along the motor shaft and start softening the small gear.

Note that some amount of white powder on the gears is normal, and has in fact been argued OK as somewhat of a dry lubricant.