RE: pitts muffler coming loose.
G'day Mate,
Sounds like a vibration issue, balance your prop, I have a Bisson Pitts Muffler on my OS 160FX & have never had a problem with it coming loose, I don't use any gaskets or locktight, But all my props are balanced using a Du-bro balancer. It will also save a lot of radio & fuel foaming problems, if the vibation level is kept to a minimum.