Cummins isx500 with exhaust manifold leak

[Kevin111]

I have a 2002 volvo 770 with a cummins isx500. I've noticed when on the boost there is a little noise from the engine that's hard to describe. I started looking around and found a broken bolt holding the back exhaust manifold to the block. There is some soot coming out but not horrible. The other bolts have rust on them so I'm sure getting them out I'll probably break several others off in the block. My question is if I'm going to be getting a new truck in about 100k miles is it worth it to change the gasket or will it get me by? I don't tow heavy, mostly 20-25k lbs, but don't want to blow out the gasket and be stuck somewhere. I still have full boost (as near as I can see) but don't want to mess anything up. Thanks for any advice.