What are some things to look for when evaluating a 1.8T? What are the most common mechanical failures on these cars? I have a friend looking for one, and would like to give him a heads up on what can go wrong with them. Something like the buyer's guide on 20v.org would be nice, but a list of suggestions from here would be even better due to the interactive element - we can more easily ask questions here. :)

He is looking at B5s, but is open to newer at the right price, and would likely upgrade to stage 2-ish type mods after a bit.

Oil starvation is huge on the 1.8 sludge problems as well. a lot of people don't use good synthetic oil such as mobil one and starve the cams, rods or turbo. Either that or they have sludge problems. Find a 1.8 that has had regular synthetic oil changes.

timing belt tensioner/pulley (45k)
oil sludge issue as previously mentioned
control arms
tire rod ends

What do the dealers put in at the scheduled maintenance?