If you use 8231's, be sure to use the SA version. The metal gears are so small that they get shaken to death, especially on ailerons, and the teeth are so fine, they strip with just a little wear. The wear increases very quickly; a little slop leads to more wear, more wear leads to more slop, and it happens very fast. Happened to me at a contest last year. Three or four teeth stripped in flight. Fortunately, I was able to get it back on the ground in one piece. Replaced the gears with plastic, except for the output gear, and didn't have more problems, since the plastic doesn't wear. After seeing this, my next plane had 9411's on ailerons, but I still use 8231SA's on elevators.

Jon