Sorry to hear that. A loosening muffler or pipe combined with a broken clutch typically means that you have a major vibration somewhere.
Have you checked your engine bearings recently? These were the symptoms that I experienced when my first rear bearing failed on my OS-50 Hyper. I was using Stainless bearings which simply expanded the races rather than chip off pieces. As a result, there was no obvious bearing symptoms until I started breaking clutches and things started to come loose.
I would give your heli a complete inspection for anything that could be causing major vibrations before flying again. Check all the shafts as well as the engine, and also check that the screws holding the servo frame to the main frame are tight. The frames can amplify a vibration if they aren't tight.