Sounds to me like a problem with corsion in the aileron extensions or a servo pot going bad.

Both of those problems can cause a servo to act funny at odd times, including working fine most of the time, but randomly jittering, or missing center or responding slowly once in a while.

On your aileron extensions, are you using gold connectors, or are the connector pins and sockets silver in color? Gold connectors don't corode, so they are better when you won't be plugging and unplugging frequently (the plugging and unplugging can rub the connectors clean somtimes).

I'd pull the servo(s) and the extenstions.

Are you using 2 extensions per servo? One from the RX to the wing (where you disconnect it), and another inside the wing? If so, you might consider cutting the servo lead and soldering on long leads that go all the way through the wing, getting rid of one connection (and failure point). Obviously, if you aren't comfortable with a soldering iron, this isn't the time to learn.