PAA: Two major roshei yeshivos were confident enough in the details to have repeated in to their talmidim many times over many years. That itself gives it an incredible amount of credibility. Don’t take my word for it; speak to a handful of their talmidim as I earlier suggested. As far as Avi K, I didn’t take his comment as coming from a talmid of Rav Gorelick. Additionally he didn’t even quote the YU grad he spoke with as denying it but rather saying the obvious that Rav Gorelick wouldn’t be mevaze a talmid chochom. The YU grad obviously felt that means he couldn’t believe the comment was made; but that is merely an extension he didn’t claim to know.
29 years ago is a short time. That sefer (as well as the next one you cite), I believe, is a zionist publication. Even R. Kasher’s forgeries are much older than that. We’ll need serious documentation this is a legitimate letter. Where was the letter until 29 years ago? (As an irrelevent aside, the internet is older than 29 years.) The proof for the Agudah convention you’re also citing is of relatively recent vintage.
RJBS’ comment is available on tape and if I recall correctly it is at a Q&A at one of his shiurim. That isn’t off the record. And even if RJBS had been speaking off the cuff (or record), what he said is what he said.
The fake KK could be laughed off. There’s no need to give a serious response to a purported KK that was mass mailed to rabbis and then published in their names (in a small publication) unless they wrote back beforehand objecting to it. (And when it was republished years later multiple different KKs each with different verbiage had their signatories combined into one KK.)