I've read some word on the net that even flashlube isn't enough because the metering of the lube isn't enough.

If you're really worried about valves, go for the dual-gas system that will mix in gasoline at high loads (this is where valve seat recession sets in... at high rpms where the combustion chamber is hot and the valve starts micro-welding itself to the valve seat and chewing bits out of it).

You have to consider the source of your research and the type of kits that such observations come from... is it for the Forester mismo? Or for other cars? What kind of kits were they using? And what is the age of the cars? I'm compiling data on converted vehicles overseas, and so far, most of the problems appear to be backfiring with venturi mixers, with valve recession not reported on newer vehicles... though everyone keeps saying it will happen, nobody has shown it happening with an SGI kit on a 2000+ vehicle.