[throwawaylolx]

>Yet all the Eastern Churches agree that Mary is sinless. [..] They agree that Mary never sinned, before, during, after birth, during her life, and that she entered Heaven with body and soul intact.

Not a dogma in Orthodox Christianity.

>So IMHO, the East agrees with the West in substance, but not in form.

You don't seem to care to make distinctions between Eastern Catholic, Eastern Orthodox, and Oriental Orthodox, so maybe that's why it seems so to you.

>The Eastern Orthodox Churches, typically, will deny that they accept any such thing that comes from Rome (the Immaculate Conception is a novelty, they say) and they will deny that their doctrines agree with Catholic doctrines.

Correct, Eastern Orthodox dogma does not give Mary's birth special theological status. So if you want to refer to Eastern Catholics rather than Eastern Orthodox, you should do that rather than arbitrarily ascribing your beliefs to other denominations.