I have done two things:

1- I have lengthened the pushrod exit holes on the wing, so that the pushrods would not rub against the wing skin while moving in and out, which is the primary cause for this binding.

2- I have cut a strip 2mm wide off the elevon, full length and flushed the top surface. There's still zero gap on the top surface, as the elevon neutral position is at 3mm up.

BRG,
Chris