You are probably both right. However the long term fix is to replace the manifold. I think it's around $672 for a new one from fcpeuro and a rebuilt one on eBay is about $350. Just depends if you want a lifetime warranty from fcp or just a one year warranty on the rebuilt one. Basically boils down to how long you want to keep the car. If you just want to drive it for a year or two, then if it's just a gasket problem then you're probably fine for that period, but as others said, eventually the flaps fall apart and grenades your engine. There's several youtube videos about how to do the gaskets and making sure they don't move.

Mercedes E350 2006-2011 M272 V6 Engine Modified Intake Manifold & Gasket Set | eBay
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Mercedes Intake Manifold Replacement Kit - Pierburg 524551
Mercedes Intake Manifold Replacement Kit - Pierburg 524551
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