oil sludge and rings carboned up can be totally prevented from happening by using a synthetic oil like mobil 1.
To understand this mobil 1 has a much higher heat point at which it will break down and carbonize. So in the ring area, standard oil simply burns up from the heat, turns to carbon and sludge and coats everything.
Make sure the PCV tube is not clogged. Try blowing thru it.
Also when the motor is running, take off the oil filler cap and see how much crankcase pressure you have. My own 98 zetec has almost no blow by. It has a very very light pressure that feels like it is pushing and pulling a little.
