Definitely cambelt and definitely make sure they change the alternator belt at the same. Get confirmation of this, We just paid £7000 in Switzerland for a new cylinder head for our T5. Cambelt had been changed at the suggested time/mileage, but the alternator belt failed and bits of it got tangled in the cambelt... and the rest is history. If I were you, I'd get the alternator belt changed every 25,000 km, which is the recommendation from VW Switzerland. VWUK customer sevices are rubbish - when I said I thought the altenator + belt should be upgraded from what is used on the standard T5 transporter to accomodate the extra demands of the leisure batteries, they just said I shouldn't be running the leisure batteries down to low %ages. For God's sake, what are they for if not to be used. VW garages are not a lot a better - lots of showroom staff and everything behind closed doors, and unbelievably expensive. It's a nice vehicle (but not perfect), but I'll never buy anbother VW. Vote with your feet!