Exhaust problems
 

After I noticed my car sounding louder than normal, I checked and found that one of the nuts had fallen off the stud in the exhaust manifold where it connects to the DP, plus the thread was messed up on it. None of the parts places in town or Lowe's had anything that would even fit, so now my car is down till I find another one. If anyone is wondering, its a 12mmx1.5 stud, and it appears that its a good bit larger than most other metric studs used in cars, at least the ones parts places carry. I noticed that the gasket was totally vaporized. There wasn't even a trace of it there. I assume this is because they werent meant to withstand flames, but is that normal? Also, what temp rating gasket sealer should be used there? I also noticed that there was an open hole on the bottom of the transmission right behind the oil pan. It normally has a plug in it, I think. What exactly is that, and would not having it there cause any harm.