As far as the Knob/Threaded bolt go.. I've been lucky.. but after fitting a new rubber washer last week I can see how easy it would be to lose a pressure fitted knob. In my memory bank.. I inserted the following notation. Buy an internal muffler of appropriate diameter & re tap the thread to suit.I'm sure it can be done easily.. Cheers
I can see tapping in a small screw from the side.... Camco style... as being a good fix too. Hmmmmm