I just saw a video about a Nissan truck where you can't get transmission parts -- you can only buy entire transmissions. It's outrageous. Seal leaking? Time for a new transmission!
Yes that video from Dave's shop has been making the rounds. Its definitely a problem but honestly if the seal was removed and the exterior, interior, and depth were measured it can be purchased by spec instead of by a parts match for the exact transmission. That's like saying a furniture company won't sell me a screw that I lost, so the cabinet is worthless. I spec what kind of screw I need by taking a sample of another or measurements of another and go buy a generic screw.