When I had the throttle body removed for cleaning I noticed the upper intake had quite a bit of wet looking carbon on the surface of the plenum. I've seen shops hang a bottle of Seafoam from the hood and let it slowly drip into the intake hose just before the throttle body to clean the intake. Any thoughts on this or must I remove the manifold and clean it with solvent and bore brushes?

 

I can't imagine that method would thoroughly clean the intake everywhere. If you go through the trouble of removing the intake, consider taking it to an automotive machine shop and having them do the cleaning. It'll come out cleaner than you can get it and you won't have to spend 5 hours trying to clean it using carb cleaner at $4/can.