There is no way to look in the wing and check it and there is where trust for the brand comes.
Be sure SkyMaster even if they are away for the JP they have been informed and will check the qc.
As for the MB339 wings ...i would like to know too what year this model came out from the pipe line .

Staale nothing is perfect..but since you are not new around
you must have noticed the progress in this products lets say with 6 years before.

Skymaster take onboard this promblems ,learn and get better every time.