The aforementioned letter referenced here would be a good start: Kengor focuses on a KGB letter written at the height of the Cold War
That's not what you said. You have the proof or you don't. It can be inspected and verified or it can't.
They had "documents" on Bush's service too. We all know what happened with that.
You said "PROOF". Not even the lower standard, "evidence".
When I see the alleged "proof", I will be able to ascertain it's validity.
So far, this story doesn't smell right.