Well, I've just borrowed a mass airflow meter from a friend, fitted it and hey presto, no flat spot. It makes you wonder if there was actually an air leak at all or wether they just believe exactly what the test equipment tells them and nothing else. Anyway, I'm now on the look out for a replacement airflow meter as my mate wants his back. Bloody nerve. Before you change the gasket I would definitely recommend this first. The borrowed one was of a 156 and was identical.