This thread came up while searching for info of a knob leak, just wanted to add my experience so it might help others.
I've had this for ~20 years, just got my 2nd bottle, so I assumed when it leaked gas & caught fire from a hole in the red knob, that maybe the new bottle was at fault, it wasn't.
So I searched for a fix, watched a 17min vid (parts) where the guy had a similar issue & duh! plugged the hole. Dumb. The gas will just build up in the handle & catch fire in a bad way.
Another useful vid showed how to pull it apart, a sharp knife then a wide screw driver to gently wedge the handle apart, be sure to tape the trigger in place.
The red knob pulls off with prying, inside it is a spring & metal pad that pushes against a rubber diaphragm, but you have to unscrew the brass housing to see it.
Using soapy water suds to id the leak, the diaphragm was perished & leaking gas. I couldn't remove the diaphragm without damaging it, there may well be an o ring under it? if so then my fix may be risky. I do not recommend you do this, for a bit over $10 you can buy a Chinese torch replacement online, the fix takes ~1hr.
The diaphragm looks like a round puncture repair pad, so cleaned with meths/glue, added some flexible rubber sealant around the ring/patch, put it together, put aside for a few days & seems to work fine, no leaks.
Also came across this adapter, seems like a good idea.