300 degrees Celsius is only 572 degrees Fahrenheit. You can barely cook Pizza at that temp
Doesn't make sense to say that 300C is overheated
One of my C&B Grass Green Perf Dlx has bad crazing around the entire circumference of the bowl and badly melted rollers. Of course Weber CS, in the USA, is very very good about replacing damaged parts. Sooooooo, if your crazing is isolated to the fire tube side of the bowl, then something probably left the Touch-n-Go starter "lit" for quite some time, or, it had a excessive flow of LPG that caused flames from both ends of the tube
I can't explain why the thermoset table survived, but I'd watch your start up very carefully for a while to observe any strange flames !!!
BTW, I still use the C&B, crazing and all, she cooks just fine and she looks kind of rugged
SJ