He stated that he knew his local dealer / tech and they would have replaced the part for him. Not exactly sure what this means, though. Techs are required to meet certain criteria in order to warranty parts. They don't just go replacing things because they think it's a problem. I've learned this the hard way.
The techs / service advisors get paid by actually replacing / fixing things that are legitimately broken. They have to send the parts back to VW once something is deemed replaced under warranty. A Dealership wouldn't just replace something because you think there is something wrong. It could leave them liable if there was nothing wrong with the part. Never seen this happen regardless of how well you knew the tech. This is why dealerships are so strict about warranty work. It's gotta match up.
Bottom line is the part has to meet the criteria of which VW has established to be deemed replaceable under warranty. You may know there is a problem, but unless it's in line with what VW seems to believe is "warrantable," then the dealership probably won't be replacing the part. Now, if the car is slinging coolant everywhere and there is an obvious failure, they will take care of it. It's essentially the manufacturers way of saying "no car is perfect and some of them will leak a little bit... we aren't fixing those. We are only fixing the ones that are really bad." Shitty, I know. But it's the truth.