Re: Used to- auxiliary verbs.
I get corrected on this one all the time.
"I didn't use to" SOUNDS exactly like "I didn't used to" as does "Did you use to" sounds like "Did you used to." Since we say "I used to" in the positive it feels logical.
(Back to a prior post with how things sound being easier for me than how they look...)
I need to keep reminding myself it's like "Did you ran" instead of "Did you run" when I want to type "used."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.