I have always believed to get the maximum benefit out of synthetic, still change it every 5-8000 kms like it is dino oil. VW's Factory suggested maintenance schedule is every 15,000 kms, on cars that require synthetic, but I still do an oil dump and filter every 7500 kms in the middle.
As others have said, regardless of the quality of the lubricant, they still get full of contaminants. The oil is the blood of your car, and the cleaner you keep it, the healthier the car is. The bottom line is, you can spend another $120 - $200 a year, to add years of life to your engine. Even if you don't keep it that long, your will get all of it back when you sell it, because it still runs like a top, and you have a pile of receipts for synthetic oil changes. When I look at used cars or bikes, I won't even consider one that hasn't been maintained on Synthetic lubricants.
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