seems you've ran into one servo of this batch
. Unfortunate that there are still a few 'out there'.
unfortunately its a long wait due to shipping,
It's easier to talk to strat and come to an agreement, then open up 'classical servo window(s)' on the bottom wing face and get rid of defective servo (least stress to the wing skin is to dremel carefully out old ones and replace with new, hopefully good ones) and then enjoy this great flying DLG.
Good luck and Success!