I had a squeaky rear seat 2nd row passenger side. I pulled my hair out trying to find the solution, including taking apart the side lever the folds the seats down,silicone the cables and pulleys, lithium grease to the floor anchor attachment, lubrication of the leather/plastic interface, silicone to the head rest poles, etc. Every time I thought, "Now, that should do it!", I punched and jiggled the backrest and damn, the squeak would not die! Finally, on a lark and and act of desperation, I placed some duct tape on the rear floor anchors where the seat hinges down and locks into place. The squeak went away IMMEDIATELY!
At least try this as a quick diagnostic test. It just might work.
At least try this as a quick diagnostic test. It just might work.