Probably a silly question, but one I feel I ought to be certain about before I act. I want to top up my oil tomorrow - it's getting a bit low. I am on fixed service intervals, but I'd like to use the best oil I can get. Can I use an oil that meets the VW 503 00 spec (long life for variable servicing), or do I need to use one of the other oil types?

Yep.

Had to ask - someone tried to spin me some nonsense about long life oil needing longer to "run in". Slightly flawed logic I thought, but I'd rather be safe than sorry! Thanks

VW 503 00 (eg Castrol SLX Longlife 2) is the best for your engine, and is what was in it from the factory, but what have you been using since? If the dealer used a VW 500 00 or 502 00 multigrade high lubricity oil, there isn't much point in topping up with a Longlife oil. You might even have a straight multigrade oil (VW 501 01) in the engine, in which case stick with that until the next oil change.