Check Engine Light (CEL) is lit & steady and running rough.

Cylinders 1 and 3 are on the driver's side of the engine. number 5 cylinder is middle cylinder right side of engine. if the engine has a blown head gasket it would be that both head gaskets are blown which would be odd. Get a second opinion preferably from a repair shop that specialize or have extensive Porsche knowledge. He a simple chemical test called a block test done, it looks for the presence of carbon monoxide in the cooling system which would only be present if the head gaskets were blown. Don't drive the car if this is the case as more serious/expensive damage will occur.