What about the wiring access grommet between the engine firewall and the driver side wall?
thanks @sjalabs..I’ll check!!!I believe that is a rubber bumper from the rear tailgate. Look along the doorjam area on the tailgate itself. It also kind of looks like a rubber inner body anchor used to secure mudflaps. The toyota dealer parts dept guys are usually very helpful, they can sometimes tell you what stuff like that is off the top of their head.
I was responding to the comment about the "inner body anchor used to secure mudflaps"..I was going to have a good look around the bottom of the bumper and the wheel wells!??? wait, I thought you'd ruled out a back door bumper like 20 posts ago, just now you are going to check?
Or was that said in jest, because sjalabs clearly hasn't read the thread?