turbo noise or exhaust leak?

[JimT]

Been working back and forth on multiple projects, both on the truck and around the house. Finally got around to extracting the exhaust manifold bolts. Easiest thing in the world. All 3 were broken off at or just below the surface of the head. One came out with just a flat head screw driver in a fracture groove, the other 2 came out with a 1/8" left handed drill bit. One without actually needing to drill into it, the other drilled down about an 1/8" before it bit and came out.

On the other hand, the turbo mounting studs are not coming out at all. I don't have a torch or welder so I tried doubling up a nut and that was a no go. Now I'm working on slowly drilling the broken stud out. Used one of the nuts as a centering guide for the drill bit so it's about as centered and straight as can be.

Can I get away with just replacing the broken stud, or do I need to replace all 4 as a set?