2.0 TDi losing coolant

[pugboy]

Hi

My wifes 2003 Touran 2.0 TDi is losing coolant. I'd estimate it goes from full to tripping the warning (bottom of bottle) after about a 1000 miles. So that's not a great deal, but still a concern.
I have looked inside the oil filler cap and there is no mayo at all. The coolant itself also looks fine and not discoloured.
There are no drips that I can find - I left it running on the drive for 10 minutes without seeing a single drop.
I cant see any water leaks on the radiator. A few chips as you might expect, but no green patches.

Looking on the web various things have been suggested:

Small leak on to the under tray which you wont notice.
Cylinder head issue.
EGR cooling (didn't realise it used water for that?!).
Water pump issue.

Its due the 80k cambelt change this month so I'll get the water pumped replaced then.

I recall when I had my Passat 1.8T they were prone to leaking on the corner of the rad and a small amount of rad seal sorted that (I only put in a quarter of the bottle at most). I worry about using rad seal long term though in case it clogs up the water pump or something.

What do people think?