Its a data point for sure, but I would be willing to bet if you researched 1/2 VW performance over the decades, there are issues with them, too. Nathan did state in the YouTube chat that the engine model-type-code indicated the engine was manufactured in 1984 and that they were stock heads/valves. There have been numerous revisions throughout the years to the Vanguard 23 HP engine and would be willing to bet some of those relate to the heads & valve train. That said, performance parts should be considered and there are manufacturers out there that make aftermarket valves (titanium or stainless steel) that would a suitable upgrade for engines running up to 4000-5000 rpms.
At the end of the day, you need to do what you feel is best (and safest). Les Homan has put quite a bit of time on the BSV23, and they have been flying overseas for decades without significant issues.
