Yamada Sensei is still quite alive.
Curiously, since Tohei Sensei just passed, Yamada is the only still alive as the letter concerns.
I'll go ahead and say this, and it's really just a matter of opinion based my experiences and those close to me, as well as conversations held with those same people:
K. Ueshiba, Tohei, and Yamada are the first generation students of the Founder. To say that Aikikai has become somewhat questionable and controversial is not entirely correct. It's more correct to say that it started that way.
I say that with respect to all members of USAF and Aikikai. Of course, I am open to discussion about the matter, for whatever my words are worth to anyone on the subject.