My up pipe leaks were bad enough to soot up the firewall insulation. The pipes also had enough of a groove worn in them to replace. Then broken bolts and a broken easy out (ha) were enough to get a new collector. Consider the bellows!!!!!
I also found a drivers side manifold leaking, at the rear. I really had to look but could see soot around the bolts. All this with about 195k. If you think you can hear them, they are probably leaking.