I know about it, it was a rumor.
Jay Leno's mentally unstable idiot of an agent (whom he fired) started dropping hints about it.
Leno fired her. He didn't so much care when he got Carson's spot, as long as he got it, and knew it would be his whenever Carson retired.
Security in the future, he was or would have been content to keep waiting, and make no bones about it, since he was going to get paid guaranteed.
Its no secret that Carson, personally, preferred Letterman.
Leno didn't fire his agent, at least not right away. She was with him during his first year or two at The Tonight Show. She was nuts alright, and had one of the most tragic stories I have ever read. She died long ago and I'm not sure if Jay ever actually fired her. Un-friggin-believable story.... I would have gone nuts, too.
Her name was Helen something. If you have the time and inclination, you can probably find her story somewhere on the internet, but be prepared to get depressed.