Gentlemen - before this gets heated - let me mention that it's a steel oil pipe.
Of course, this thread has just made me think about the implications of it being a steel pipe - like there was probably a sealing washer in there that I've lost.
Lost it several years ago in fact, when I had to do a head swap (an exhaust valve stem broke, struck a piston, ensuing carnage - all at
40mph tootling home from work, 2 weeks after buying the van, 85K, dealer maintained - these things happen. I thought it was a cambelt failure at that moment, but really was a spontaneous valve stem failure on an otherwise fine engine).
Of course all this happens 2 weeks before I go self-employed (hence buying a van), so I obtain a cheapy recon cylinder head, dremel the worst of the damage out of the piston crown - and regard the whole fix as a nasty bodge.
100K miles later, all is fine. It really has been a remarkably small leak considering I lost a seal.
Now I do apologise to all the posters here for running you round all 4 sides of a square - but if it's any consolation, it's done it's job and made me think it through.
I'm going down the vw dealers and getting them to look through all the nice parts diagrams...