I don't know how to upload a photo, but I can describe the location of the missing seal, and tell you how to know if yours is missing.
Directly back of the drivers side cylinder head of the 6-cyl engine (and imagine the same location in the 4-cyl), you will see two aluminum air conditioner pipes, one larger than the other. They both turn toward the firewall and enter a kind of lump (maybe a pipe joint), which passes thru the firewall. Pick an evening or inside a garage, and place a light where it will shine toward the firewall, where the two aluminum pipes enter on the engine side.
Look under the dash on the drivers side, above the gas pedal, and you will see the same 'lump' on the inside of the firewall. If the seal is missing, like mine, you will see light entering thru the gap from the under-hood light source.
A small flashlight was all it took for me to see the light leaking thru the gap around the 'lump' where the lines pass thru the firewall.
My fear of the repair is that the freon probably must be removed and the pipes disconnected to put the seal into place. It might be possible to somehow put the seal in without disconnecting the pipes, but that would require cutting the 'mostly' round seal so that it could be wrapped around the 'lump'. But that is probably not how it will be done. I guess at this stage everything is under warranty, so if it leaks or something, the dealer will have to fix it.
I can attach a photo of the general area which shows the pipes and where they enter the firewall at the 'lump', if you can tell me how to attach the photo. But the area is easily identified by the 'aluminum'-looking pipes (about 1 inch in dia for the larger one, about 1/2 inch in dia for the smaller one).