For anyone interested, while I'm waiting for a new feeder-pipe to arrive I thought I'd try a dodgy fix with some gasket goo. Thought it might at least make a difference to the sound of the leak; maybe it might come in later, or at a different pitch.

Hasn't noticeably affected the sound, maybe it's coming in a couple of hundred rpm later. It does feel like it's getting a little more boost into the cylinders, but of course it's hard to tell and might just be me talking my hopes up.

So I'm not really any closer to knowing if the new pipe will fix the problem. Still, I f**** love this car!