When I was buying our GTi off a main dealer 2.5 years ago, I asked them to replace the tensioner etc as part of the deal. They point blank refused but told me they would replace it under the VW warranty if anything went awry. I didn't believe them.
Anyhow, after a couple of months with me being convinced the car sounded like a low volume diesel, my perception being the chain was making a rattling sound; and after persistence and a complaint, they changed the tensioner, chain and all associated components, gratis, as a good will gesture to give me confidence in the car they'd sold me.