Our 2006 Passat has oil sludge build up. My wife slacked on oil changes a few times, changing it on average every 7000 miles. VW recommends 5000 miles We insisted on synthetic oil and that was VWs recommendation too.
My Porche mechanic says the passat 4 cyl turbo was designed with to little oil in it and the turbo is likely to cook it and sludge builds up. He suggests a larger oil filter to increase capacity and a little cooling help.
I had a landcruiser I used synthetic in so I could change the oil every 9000 miles, it lasted 150,000 before I sold it.
Considering a Passat? Sludge will probably kill your engine before 100,000 miles.

By the way, they want $350 for a breather hose and $240 for an engine flush. Is that even reasonable.