I stumbled across an interesting thread in a VW forum in which two different VW owners reported they were able to reverse their oil consumption problems by simply using a retail crankcase petro-solvent such as MMO. If you read through various message boards, some VW/Audi owners can go through a quart of oil in as little as 1,000 - 1,500 miles, with some people exasperated enough to mention, "Wish I had never bought the darn car!" The problem has bedeviled more than a few VWAudi owners. On the other hand, my 2008 Passat uses very little oil, so the problem appears to exist on a car-by-car basis. Should gummed up piston rings contribute to this problem -- just one possibility -- I could see how a simple solvent might clean them up enough to reverse the problem, at least for a time.
http://www.passatworld.com/forums/74-volkswagen-passat-b6-discussion/343167-b6-oil-consumption.html
http://www.passatworld.com/forums/74-volkswagen-passat-b6-discussion/343167-b6-oil-consumption.html