I have a Honda 24 HP motor on my slide-in, and had the same thing happen to me. The weld on one side for the pipe, simply broke apart from the muffler body.
I ordered a new one, and so far no problems (4 months).
I also run an exhaust pipe, from this muffler, down through the van floor, and exit it out in front of the van's rear driver's side wheel.
Talk about quiet!
My guess as to what happened to the original one (9 months old), was either faulty manufacturing, or this:
On the original muffler, there was a lot of heat coming off of it after we shut it down, which would indicate a steel that was getting too hot.
The new muffler is not giving off nearly as much heat as the original one did.
Either way, I hope they fixed the problem ...lol
Now I see Honda has discontinued this particular motor.
I am quite happy with it's performance!