EXCLUSIVE
Multiple sources tell us, the tape owner approached the Carson estate in September to make a deal for the footage -- the estate said take a hike, and threatened to sue the owner if he ever sold it.
But the owner's apparently gone rogue -- we're told he's now shopping it to private collectors ... and it is legendary.
According to sources who've seen it, the tape was shot right after he married wife #3 Joanna Holland. It opens with a naked dark-haired Carson masturbating by a pool -- then shows Joanna (with a bouffant hairdo) going all Linda Lovelace.
It goes on for about 5 minutes -- then we're told it cuts to a 20-minute sex scene in Johnny's bedroom ... and Johnny does NOT hold back.
Oh yeah, we're also told he's hung like a horse -- seriously, porn star status. One source said it was at least 10 inches. But for legal reasons it can't go to a porn company, so the only way to unload it is with a private collector.
Move over Michael Fassbender.
