Exhaust leak...broken bolt on header?
#12
It wouldn't hurt to spray some good quality, penetrating oil on the bolts about a half hour before starting the job.
#14
GL
#16
drill the bolt on center all the way through, with a bit smaller than the bolt, then soak with pb blaster and use an extractor to remove. If it still wont come out, drill it the size of the bolt, then tap and helicoil.
#19
ARP makes a stainless steel stud & nut kit.
#20
I used a stock replacement because I already had a cat-back exhaust. The long tubes make more power, but I didn't notice any substance increase in the seat of my pants. All of my mods as a whole made my 3.5L come alive.