Here are some measures I have done that will fix or either greatly eliminated your exhaust leaks that seem to plague the dubbers.
On tube header, the slip joints tend to stretch out over time from assembly and removal. The carbon does tend to build up in the leaking area, but really, who needs that? One cure is to take a Dremel with a small cutting disc and cut a 1" to 1 1/2" slit on one side of the overlapping slip joint running parallel with the pipe. This frees up some slack on the pipe. Once done cutting (non-ceramic), slip over the cut pipe using some milk of magnesia. Once secure, use a pipe clamp over the slip joint to take up the slack from the cut. This will cinch down over the inside pipe and cure the leaks.
Another way is to use the high-temp RTV (copper-color) in conjuntion with exhaust gaskets. I do not use the stock gaskets that come with the kits. I use the solid copper gaskets that can be slipped on over the bolts without having to take the header off. Very handy...
Hope this helps...

Dave

Thanks Dave, great advice!

Thanks Dave,would have never thought of that.

Permatex makes a mufller/exhaust sealer. Good to 2000 Degrees!