Here's a link to the information that has been collected by the rear wheel drive Volvo folks (owners of the 700 and 900 series).
http://www.brickboard.com/FAQ/700-900/Fuel_LubricantData.htmIt provides alot of information on what type of cleaning does what and in witch way it helps. Theses guys are used to high mileage car. Being part of the 200,000 mile club is typical.
I hope it helps.
Eric