Yes that is absolutely correct as well. Boeing would not stand behind the after market winglets. That was probably a bigger deal killer than the disappointing fuel figures. I still can't remember why the winglets prevented us from using flaps 40, but I think it was because of unknown wing stresses from the mod. Once we were at flaps 30, we would put a cup over the flap handle to prevent us from inadvertently going to flaps 40. The hush kits also prevented flaps 40, but the handle was actually locked out so one could not select flaps 40 at all. Oh, those were the days. HA