One more to add to this list...
Took my car in to dealer last week about a squeak under the bonnet, they changed the auxiliary belt and tensioner- didn't solve it...
Took it back in again this week, had cam belt and tensioner replaced today, tensioner was under warranty but had to pay £38 for the cam belt.
I asked if I should have the water pump changed too at this point but apparently it's a completely different job and would've only been necessary on the earlier gti's.
I'll just take his word for it.
Happy that it's sorted now.