I had a cracked exhaust manifold earlier this year. It didn’t make any noise though. Nor do I see evidence of a crack in your photos.

 

or can I use muffler cement, from JB? It looks like it will be thicker and fill any gaps.

 

Muffler cement is kind of like putty. It's okay, but if it's soo thick it can break into chunks and fall out. Copper spray is only good for very small surface deviations so if your leaks are significant, it probably won't help. I always use it for exhaust gaskets and head gaskets regardless.

 

Maybe use red (high temp) rtv gasket maker to skim coat the gaskets, but will be a bit more difficult to clean up next time around. The steel surfaces of the exhaust can become quite pitted over time, then machining or replacement are options. I have had pretty good luck with composite-type exhaust gaskets (vs MLS) and use red rtv on the steel side sometimes.

 

The almost final solution to the noise was ocrams razor, thanks to rikkd. The drivers side junction to the header had 2 of the 3 nuts not even finger tight. With the vacuum method there were no bubble bc the gap was so big, wind was just blowing out the junction. Some antiseize and put them back together, all better. Still have a tiny leak, but atleast it is quiet. I think the fix is some muffler compound with the new gaskets. But there are no symptoms, so no rush. I do have the a slight leak at the front of the passenger side header.
If i could back off the bolts a bit on the other 3 cylinders, could I just remove the two on the offending exhaust port and replace only that gasket? Otherwise, I may need to leave them alone. It would be just my luck to do an optional repair and bust a couple bolts and have a disabled truck.

Thanks for the advice.