Leaf weather seal
A quick learner from Michigan says:
October 16, 2015
Sliding glass door of unknown manufacture. The glass is branded with"Arm-R-Clad". It appears this is an unusual leaf weather seal in that the work surface, meaning the surface that rubs against the door frame, is parallel to the kerf, rather than perpendicular to it. If you get my meaning. The second photo shows it mounted in the channel through which the door top slides.
Dave from SWISCO responded:
October 20, 2015
Arm-R-Clad is a very old type of tempered patio door glass. I'm assuming that the door in which it is installed is just as old. I'm not sure if we can get an exact match, but look at our 58-175 and let me know if you could use this as a substitute.