Had a 1000cc 48,000mile Corsa in this week with a misfire. The customer insisted that I check the manifolds first as he was convinced that the manifold was causing the miss. We did so knowing that this wasn't the issue but following customers instructions we smoked the manifolds and no leaks. I then asked him for another half hours labour as you could hear the engine was lacking compression. A compression test a cylinder leak test and pull the cam cover of and the inlet cam was bust in two. Cylinder 3 inlet valves are never going to open if the cam if not attached

You should not expect that at less than 50,000. Oh well it keeps us in work