I found the same crack on my exhaust manifold as well. Just a hairline crack, and would not have noticed it, but did after cleaning and polishing it with a wire brush wheel. Also had a broken manifold stud. I ordered a new manifold, and am also replacing the motor mounts since this could be the reason for the failure.
What brought me to the exhaust side of things? The exhaust at idle smelled rich. My NOX value has been creeping higher on the smog test. CA is every other year. I thought I was going to change the Catalytic converter to solve the issue, but research told me that's not what to do. If a Catalytic fails, it's because of another issue upstream. This is when understand how to use a scan tool is crucial. Using LTFT and S1-O2 sensor values is what led me to searching for the cause of unmetered air entering the system via the exhaust side. At idle on a warmed up engine, my KA24E values are: LTFT 14.5% S1-O2 0.780V. And sure enough, I start working on disassembling the exhaust manifold and I find the broken stud and cracked manifold, the lower gaskets were also on the verge of disintegrated as well.
So the new manifold is on order from Rock Auto. I have a new O2 sensor ready to install as well since I got one on clearance for $20. My old one is worn out. I'll post back after I install the new manifold. Hopefully this will bring my LTFT value down into acceptable range of under 10%. Factory perfect is less than 5% LTFT.
By the way, this guy has a great series of videos teaching how to diagnose using a scan tool. Check it out:
https://www.youtube.com/watch?v=5WnM_Ns ... Vg&index=3