Flywilly.. My first OS 1.20 AX had the same failure. The muffler bolt broke in flight. I thought I lost it for good, but we took a walk and actually just about tripped over the darned thing.. the rear half, intact, broken bolt and all.

I bought a length of all-thread and put that in with a nylock nut. Worked just fine. In the mean time, I notified OS about the problem and they immediately shipped me a replacement bolt.

I have two other OS 1.20 AX's and neither of them have lost the bolt, and I fly them equally as regular as I do the Excelleron 90 with the original 1.20 AX.

BTW, the other two are on a Venus II and a Goldberg Tiger 120.

CGr.