I had DMH cutouts on my 2007 Charger Super Bee. Everyone on the Charger forum with the DMH cutouts had leaking issues. I don't know if it is still the same problem or if they've made design changes since then, but the gaskets from DMH did not last long. After everyone bitched DMH came up with a replacement, and those didn't last much longer. For a while they quit supplying gaskets and sent a tube of copper silicone instead. I wound up making my own gaskets. I bought a sheet of exhaust gasket material from Mr Gasket and cut them out myself. This sheet has an impregnated metal mesh core. I think I got it off Ebay or Amazon.
Unless they've changed their assembly practices, you also want to disassemble everything you can and put it back together with Loc-Tite.
Here's what I wrote 2 years ago on the Charger forum:
"I have had the DMH exhaust cutouts for over a year. Here is what I have learned with them:
1) The supplied gaskets burn out very quickly. Mr Gasket makes a steel mesh reinforced sandwich hi-temp exhaust gasket sheet. Get this and make your own gaskets. If you hear a hissing noise while the cutouts are closed, your gasket is fried and a chunk is either missing or hanging down and not allowing the valve to close all the way. It does not take long for the original gaskets to break down.
2) You need to take the cutouts apart and put them back together using threadlocker. This includes the four screws holding the motor assembly to the valve assembly, and the two set screws that hold the butterfly valve to the shaft. The rattling noise is due to the set screws no longer holding the butterfly valve to the motor output shaft. I actually lost two of the screws due to vibration, and I have had the rattling butterfly valve issue as well. Threadlocker should take care of all of this."