Good methods to clean extruder gear (hobbed) from filament pieces?
If your gear skips at the same place each time I have found on my machine that the gear does not fit the motor shaft properly and has a larger gap between the gear and the idler roller.

Check to see if there is a thicker buildup on one side of the gear than the other.

On my machine what I had to do was to use a spare motor cable and watch the gear as it turned, and at one point on the gear it would slip and shave off a small amount of filament. 

If that turns out to be your problem use a good caliper to measure your motor shaft, and the inner diameter of the gear. 

Sometimes the minimum shaft diameter and the maximum bore diameter of the gear are just enough to allow that small variance in the outer rotation diameter of the gear.

Sometimes just replacing the gear will solve the problem, and sometimes it will require a new motor and/or gear.

As an alternative you can clean the gear using Acetone and a toothbrush, but that will be required often and you will have buildup in the chamber below the gear which can also cause feed problems, and you must make sure that all Acetone has dried before using the extruder again.

I suggest starting with changing gears since they are the cheapest and using the Caliper to find the closet fit possible. 

You can get gears on e-bay at very reasonable prices. and I bought several to get the best fit possible.

Good luck and consider if you want to make a more permanent repair or temporary repair when making your choice. I chose the more permanent one because the slippage was affecting some of my prints.