On Sunday, May 27, 2018 at 10:03:05 AM UTC-5, wrote:
It could be a warped wing, there was an article years ago in Australian Gliding detailing a similar problem with a Mosquito, which was cure by heating the wing in a large oven whilst twisted back
allowing it to cool a couple of times.
Ige seen small aluminium tabs on ailerons used to correct minor issues.

Boy, am I hoping it's not a warped wing.

Wing tape is already in use, cleanly applied.

Taped up the inspection ports and am next going to figure out how to seal the apertures around the control rods (it has has the first edition push-pull rods instead of the snap-together twist rods). Will see if that makes a difference and report back. Not going to mess with turnbuckles until we determine that it's not a differential air leak or vacuum.

Cheers,
Chris