@ChuckOman, I merged your post here, because your issue has already been discussed and the problem has been fixed yesterday, see the solution a couple of posts above.
Downloaded the latest standalone manager, and installed it on top of my GSX v1.9 install and indeed my couatl engine problem disappeared. Appreciated your rapid response ! Many thanks.
BTW was I correct in assuming that the LVLD_B763_Winglet version is not natively supported under GSX, and so winglet users do have to create a GSX.cfg file for it, and install it per manual instructions ? Or has LVLD_B763_Winglet native support been provided, even though it isn't on the supported list ? If a GSX.cfg file for the winglet is needed, I can report that the file I attached yesterday works fine for the winglet. It was based on the non-winglet airplane. Adding the winglets didn't change the GSX relevant geometry, apparently.