Okay so Minato says the seal stays on forever. But here's the problem I have with that. Didn't Minato plant the seal on Obito's other robes and not directly on him???
The rasengan to the back (part of the flying thunder god level 2) tore off part of his back and Minato was able to plant one directly on his back. Good question though
I just want to know how he knew it was the same guy after teaching obito for years then fighting him doesn't recognise but sees him uh diff clothes no mask i call BS