It honestly looks like the reflective piece on the top has got a little too hot and started to melt a little.. Of course pictures can be pretty deceiving sometimes!
I would probably take the bulb from one of the other two that you know are good and see if it has the same result. I personally haven't seen a normal halogen bulb used in our tail lights get that hot, so hopefully it's just the bulb that has a little black spot on it or something!
I would probably take the bulb from one of the other two that you know are good and see if it has the same result. I personally haven't seen a normal halogen bulb used in our tail lights get that hot, so hopefully it's just the bulb that has a little black spot on it or something!