That's sort of bad advice, Sif. The oil itself will NOT cause leaks. What does happen is if, by some chance, your engine has a bad gasket, and has been fed fossil-based oil all its life, the ash can form a "plug" around the gasket failure area, kind of like a clot. When you switch to synth, the clot will break up and go away. This will show you actual bad gaskets that will need to be replaced, because your new oil will seep through. Never fear. Synth is FAR better for your engine, and can last over 10K miles, although swap filters at 5K. In fact, do not change synth as often as you change standard. Synth oil becomes better as it ages, up to a point.
