Yes, had the same trouble with the muffler. OS is better, but the pressure nippel tended to unscrew. Now its soldered.

Thanks for the input with the flex pipe, I will try that.

So the fuel should be fine.
Have you tried playing around with the low speed needle? Even if transition and idle is fine, just a small change could be an improvement vibrationwise.
I tried several props, also light wooden ones. Made no difference in vibrations, however the idle was a tad smoother. And they have to be balanced, of course.
But the best advice, I guess, is to bolt the engine as firm as possible to the firewall to lead the vibrations into the fuselage.

Cheers
Andi