Well the first top that cracked on me that I found on friday may have been from over tightening, but today I looked under my system and found a puddle of coolent coming from the second pump. After removing the pump and top I found a small crack away from any screw hole in a solid part of the top. These new OCLabs tops are not mach. but molded and are very thin walled. The XSPC tops and the like are mach. from thick stock. You can say what ya like about plexi, but I will never use it in any of my blocks or pumps again.