Bil, it might be me, but it looks like your ailerons are not getting the same throw ... the angle in which the left nirod is connected to the servo will give it more pull and less push then the right one ...

But if you say this works for 10 years ...
Maybe the servo is not at center position when the pic was taken ...
It will still give you an amount of aileron differential ...

Am I wrong?

Yakir