I had a bad leak experience with synthetic. It made my valve cover gaskets start leaking on my Passat almost immediately after I switched at 24k miles. It was never the same - they never quite fixed it, they tried 7 times and replaced the gaskets 4 times. Never mind, that will soon be in the past as that lease is over soon. One thing about synthetic though is that my veedub did not use any oil with synth while it always does on dino. I will probably use synthetic only if the car started with it or if it's early in a cars life...