whoever told you that is living in the 70's. modern synthetics are 100% compatible with dino juice and all engine seals and gaskets. switching back and forth between dino and synth will cause no harm to any seals, gaskets, or the engine itself. the synthetic will hold oil pressure better at low speeds and hot weather, which is good if you are stuck in traffic. more oil pressure means a happier motor, because no metal to metal contact occurs. synthetic will not harm the motor in anyway. actually, the sportie likes synthetic, as people here have demonstrated. and you do not need to "flush" your motor out before switching to synthetic. mechanics nowadays will try to pull anything over your eyes to make a buck, and in the process they will actually make you believe that what they are saying is true.

matt
Mobil 1 10w-30