[rluvsbenz]

I finally had the guts to adjust my valve's on MY78 during the weekend. Although I haven’t had the chance to start her up because I'm still working on swapping exhaust for new SSI's and M&K duals. I found a broken cylinder head stud lying by number three cylinder. Don't know when this happened. I don’t have any engine performance problems that I know of the cars runs good and strong. I've owned the car for 28yrs so sure no power lost.
Here are my questions.
What will happen if I don’t fix the stud?
What will it take to fix this problem?
What will cost?
I have lots of carbon build up on exhaust cylinder 1&3 and the rest are clean.
What can I do to clean the carbon?