An FBI liasson to the Executive Branch would hardly be in a position to even know about Nixon's secret White House recording system, much less know about the gap on the tapes.
First, as the #2 guy at the FBI which was investigating Watergate, I don't know that you can say he didn't know about the tape system, and he only needed to be able to learn of all of this information-- not hear it first hand.
But, fine, just keep thinking it's Rehnquist. When Felt dies and Woodstein confirms it was he, then you can just pull up this thread and say I was right. If they don't then, I'll do the same.