Even if it doesn't fix your problem, consider valve replacement as preventive maintenance. They can and do fail. I had one fail at around 35k miles under warranty. When I hit 120k I went ahead and had a new one installed.
Interesting about your results with Seafoam. It is supposed to reduce intake deposits on valves and such. I run a can of Lubro Moly "Ventil Sauber" in my gas tank every 5k miles or so. When I had my valley pan gaskets replaced the tech said my intake system and the ports into the intake valves looked really good.