I reckon this is on your '51, right?
Glass is tempermental and can crack just by looking at it. That being said, the crack could have happened when the door got shut. My passenger door window did that in the lower rear corner after shutting and it wasn't a big crack, maybe 2 inches long and in a sideways sorta circular V with the point of the V going forward. Is the crack a big or small one? Myself, it's always best to find a local guy if you can, for obvious reasons.
