2000 GMC Sierra Manifold leak

My Manifold has a leak and the bolts are very badly rusted. The mechanic said to just leave it alone but I feel differently. What about using JB Weld or something like that. I know it doesn't have a gasket so I am really trying to figure out how to stop it from making the annoying clicking type sound when I accelerate. It seems to get a little better once it warms up but doesn't entirely goe away. Any advice on what to do??