From my experience you really have to go with the manufacturer. Not all valve seals are the same. They have different angled sides, ridges, and flares. I have had no luck getting any replacements from Thomsen in Kenosha, they are "restructuring" is the only answer I get. Definox has been a bit better in that they will supply me with the name of a local dealer. The first of which I called and they had no clue who Definox or Defontaine were. The next time I called I asked for a list dealers.
CBO "Chief Brewing Officer" / Zymurgist
Bluegrass Brewing Co
636 East Main St