Broken quarter windows fastback

[Ted S]

Why do the quarter windows brake on the fastbacks. Seems to happen allot. I just bought a replacement , but will it brake too? Driver side is ok. Just the Rt side is broken.Anyone know why?

 

[melsg5]

the general theory is that temperature changes eventually cause them to crack, seems like the original design did not leave enough clearnace to account for changes over long periods of time.