. . . and there it is in writing, Amphicar770'* Terraza has been consuming at twice the expected (and awful) rate.

These types of things just make GM look bad. Cars have been expected to hold most of their oil for decades, give or take leaks and abuse and defects. Blaming this consumption on cylinder-wall residue is sad. I have decades of GM in my driveway mostly in the 200,000-miles plus range that all loose less than a quart in 3,000 miles give or take a couple of them that will lose slightly more while being decades old and working hard.

Sorry for your bad experience with this Terraza Amphicar770. All I can say in favor of GM here is they are doing a lot better now in my opinion. As are many other manufacturers for that matter. That having been said, if I were manufacturer-neutral and looking for a minivan and didn't want a crossover (like the Acadia/Enclave/Traverse/Explorer/MDX/etc.) I'd lean heavily towards the new Chrysler Pacifica. It'* their replacement for the T&C and has their wonderful FCA 3.6VVT and a 9-speed transaxle. The T&C/GC were already great minivans with the 3.6 and the 6-speed (I've rented lots of these), the Pacifica should be waaay better.