First I want to say it is from my another car but I guess this case is universal about patching manifold. If moderator feel it is inappropriate here you can remove.
Well I have for a while puff puff noise from front of truck passenger side. Per internet it is manifold if is puff puff. I know why is puff puff. It is because crack is close to one of cylinders and that one make most noise. So tried to look at it nothing. Than used spray with water and detergent, same one that use at tires. It fly right away from there. Than used stethoscope and that thing like always proved useless to me. Well can not find and decide like usually spray Cold galvanizing from Rustoleum. Old Cold galvanizing is already at manifold, and I add a new coat. And crack show up right away. I used water spray and bubbles was there.

So what is best way to patch this crack? Would not do replacement of manifold till all other options proved useless.

 

^^^ Just who may interest. Patched it with combination of Menards furnace cement and piece of metal hanger strap. Hold well. However noise wasn't from there than from loose flange.