valve seals

[Fast350ex]

How do I know when the valve seals are bad?

My 400 is leaking oil from right underneath where the pipe bolts to the head. Is this bad? Could it be the valve seals?
It doesn't make a puddle on the ground, but it leaks out and sits on the cylinder/ head fins.

[sevens]

If your stem seals were bad, I think this would cause oil to leak down into the combustion chamber. You can tell if they are bad if they are no longer soft. Sounds like you may have to replace the gasket above where it's leaking.