The Tunze regulator uses a soft rubber seal ring that is set in a groove on the regulator. You should not use any sort of additional seal such as the typical nylon washer that comes with most bottles and you should not use any Teflon tape. The only seal ring I know of that will work is the factory part 7077.310. In general, I can't think of many ways this would not seal. I have used this regulator myself for nearly a decade and I have changed the seal once, they can be quite marred and have impressions and if tightened sufficiently still seal correctly, the only fatal damage is a severe pinch or tear or being missing. In my case a couple years ago it slipped and got twisted/torn and had to be replaced. You want to tighten it to just snug and then give it about a 1/8- 1/4 turn more, over tightening can deform it or cause it to slip. The newest ones have a hex fitting and can be tightened with a wrench, the older models had a hand tightening gnurled fitting, for that type which is what I have, I tighten to snug and then turn the regulator and fitting together about 1/8 turn more by hand to get it really tight. You can very carefully use pipe pliers but be careful to not mar the fitting.
