That center shaft may have too much slop, fuel leaks through the top at the shaft. Try double down on that ms29513-10 o-ring, you might find it snugs up the adverse tolerance, stops the leak.

The valve is at McFarlane so out of my hands at the moment.

Never underestimate how aviation can turn a $25-$100 part in use in reliable marine and motorcycle circles for a century into a $3000+ piece of near unobtanium.

So a final update. The cam plate in our original valve was serviceable so out of two we made one.....

All in was around 1800 bucks. Hopefully this particular part doesn't need any more attention during our ownership.

On to bigger and better things. Seatbelts..... lol....

My update:

At annual when removing the firewall fuel screen we found that the selector doesn't 100% cutoff the fuel, there is still a small dribble that leaks. Enough to cut the engine but not to fully stop all the fuel. Next step is probably sending the part to McFarlane. humpf!