When I got 1488 eight years ago, the back window was cracked from right above where the driver side seat belt mount bolt goes through the back trim panel to the roof line. This was a single crack with no side "spider" cracks deviating from it. I have no theories of how the glass was cracked before I purchased the car. During the restoration, I bought a new gasket and had a piece of automotive glass cut using the original as a template and installed by a friend who is in the glass business. The car has an adjustable rear cross member brace installed over the ZF as many of us have and the car was sitting on jack stands with the wheels off for 2 weeks prior to the wheels being reinstalled and taken off the stands to put the new windshield and back glass in. The car has been drive on one long trip (to SE Pantera Prez Tim Clinger's house), a few docile cruises, and a few sporty ones since the install. No major driving events and only a few time in the 90-100 MPH range. The new back glass cracked again but this time it cracked more inboard from the first crack. The new crack starts just above the driver side frame rail and has 5 "spider" cracks fanning out from the bottom point of origin to the top. My glass guy says he may have made the fit too tight and will replace it no charge. I'm looking for any other theories that could explain it before I put another one in and it breaks again. Is it possible that the car being on jack stands could have tweaked the car enough to cause the glass to bind as it re-tweaked to its natural state? When I got 1488 eight years ago, the back window was cracked from right above where the driver side seat belt mount bolt goes through the back trim panel to the roof line. This was a single crack with no side A "spider" cracks deviating from it.A I have no theories of how the glass was cracked before I purchased the car. During the restoration, I bought a new gasket and had a piece of automotive glass cut using the original as a template and installed by a friend who is in the glass business. The car has an adjustable rear cross member brace installed over the ZF as many of us have and the car was sitting on jack stands with the wheels off for 2 weeks prior to the wheels being reinstalled and taken off the stands to put the new windshield and back glass in. The car has been drive on one long trip (to SE Pantera Prez Tim Clinger's house), a few docile cruises, and a few sporty ones since the install. No major driving events and only a few time in the 90-100 MPH range.A The new back glass cracked again but this time it cracked more inboard from the first crack. The new crack starts just above the driver side frame rail and has 5 "spider" cracks fanning out from the bottom point of origin to the top. My glass guy says he may have made the fit too tight and will replace it no charge. I'm looking for any other theories that could explain it before I put another one in and it breaks again.A Is it possible that the car being on jack stands could have tweaked the car enough to cause the glass to bind as it re-tweaked to its natural state?