If the exhaust housing cracks how easy is it to see?

A mate is experiencing boost drop off 17psi - 9psi after only a few seconds and we have checked all his hoses, intercooler, actuator, etc.. I'm thinking maybe a cracked housing?
It's a stage 3 T3 on a stock RST engine with a bit of port work so should have no problem holding boost at all!

Cheers!