On Sunday I drove her onto ramps for the second time this month, whipped off some of the plastic under-tray and had a good look around. Naturally I feared the worst and assumed that, while jacking up the gearbox to get at the prop, I'd ruptured a seal somewhere and was dropping engine-oil, meaning the engine would have to come out for the warped part/gasket to be found and replaced. With this in mind it was actually greatly relieving to discover the the leak was 'only' a corroded fuel pipe.
Turns out the fuel lines run externally, which is something I haven't seen before, and the metal sections are not covered by under-tray and are exposed to the elements, allowing them to corrode, although I don't know if them leaking is common. Seems a bit of a design flaw to do it this way, I mean it'd be a bit dangerous on a petrol car surely, but I guess BMW have done this to keep the noisy fuel pressure-pump [under the passenger seat] outside of the cabin on the diesel models. Mine had begun to corrode quite badly around the front pipe-bracket, obviously where it's been rubbing, but its been holding up and I guess whatever knock or shove I gave it while fixing the prop-shaft opened up a pinhole. I should be more careful when working under the car, but once you've spent two days squirming around in a tiny gap between soggy concrete and filthy metal, there's a tendency to become complacent...
It's not worth trying to repair the pipe, replacements are very cheap. I'm sure they can be found for even less, but I ordered mine from BMW Parts themselves [Part No. ] and it was only £18.00 inc. VAT anyway.
PROCESS:
Replacing the pipe is very easy. It's right behind the passenger sill, so you only need to jack the car up a little to access it, but the job is messy and diesel is nasty stuff so make sure you've got a plastic sheet down and plenty of tubs to catch it.
