^^ I agree that Rexy's evidence does not make for an open-and-shut case. But if there's a chance that she's seeing Mobil1 users running out of engine oil because Subaru's boxer engines consume Mobil1 faster than other brands, then that's a chance I'm not willing to make. She admitted herself that Mazdas seem to run just fine on Mobil1, and she thinks the problem is specific to Subaru engines.
There are many variables and questions. Is this true of the older 2.5L engines, or just the 2.0L engines? Normally aspirated engines, or only turbo engines? Is it only true of engines that spec 0W-20 oil, or is it true with other oil weights too? Is it only true of customers who bring their STIs to track day events, or is it also true for soccer moms? Or is Mobil1 just fine in all cases?
I don't know that we'll ever get answers to these questions. As I said earlier, I'm guessing that Mobil1 0W-20 is a fine product in our Imprezas. My car seems to be running exceptionally well on the Amsoil OE product, so that's my chosen motor oil. And I have no plans currently to upgrade to Amsoil Signature, and won't consider doing so until several people show me Used Oil Analysis reports that convince me otherwise. In the meantime, it's Amsoil OE on a 5k mile OCI for me.