All the cracked bulkheads I've dealt with have cracked right on the mold seams. My guess is it was a shotty batch. The main failure cause for these was external pump vibration. (I really had to dampen this down with spaflex and rubber)

Hmmm, interesting. It broke even with spaflex? I've always used spaflex or vinyl hose to dampen the vibrations from the pump but I was trying to protect the glass itself of the sump wall, not the bulkhead.

I've repaired quite a few tanks with damaged bulkheads. Sometimes cracked, cross threaded or just leaking. Never seen any problems with the good sch80s, Sch40s are good to but those cheap sch20 black ones are complete junk. Threads are too fine, not reverse threaded, think brittle plastic, and tiny thin gaskets. You're just asking for trouble using those and they are usually the ones I'm always fixing.

The money you save is peanuts compared to the rest of the setup, if you use cheap bulkheads might as well use thinner glass to and skip the home insurance. Especially on a close loop where replacing a bulkhead means draining the tank.