I have experienced my first cracked screen after 4 Mogs, 8 years and 75.000 km in total a week ago on Saturday with my P4SS. And I guess why it happened in this special case (realized the possible reason after it was to late...)We had suddenly very warm weather here in Cologne, more than 23 degrees Celsius. Down in my basement car park it was subjectively felt about 8 or 9 Celsius, at least very cold. I drove her up and opened the roof outside in the warm air. Two minutes later the crack appeared and went down from the right upper corner to the bottom in an almost 60 degrees angle, very smooth and quiet. Possibly different thermal expansion coefficient of glas and frame...No accuse just reporting and perhaps a warning, let her take her time when facing so different temparatures before doing anything on the roof or touching the frame of the screen at all...
