I HAVE TWO QUESTIONS, FIRST MY WIFES CAR IS A 2007 GS350 LEXUS WITH ABOUT 75000 MILES. SERVICE ALWAYS DONE AT LEXUS EVERY 5K MILES. NOW THAT IT'S OFF WARRANTY I WILL CHANGE THE OIL. WHAT TYPE OF OIL DO YOU RECOMEND FOR ME TO USE. IT'S ALWAYS HAD LEXUS OIL WHICH I BELIEVE IS A BLEND. SECOND QUESTION MY CAR IS A 56 CHEVY WITH 350 CRATE MOTOR 330HP AND 380 TORQUE VORTEC MOTOR BACKED WITH A 700R TRANS. THE PREVIOS OWNER USED CASTROL SYNTHETIC IN THE CAR, DO YO ADVISE USING THE SAME AND SHOULD I BE ADDING A ZINC ADDITIVE TO THE OIL. I HAVE BEEN HEARING ALL THIS TALK ABOUT THIS ADDITIVE FOR FLAT TAPPET ENGINES. THE ENGINE HAS ABOUT 17K MILES ON IT. THANK YOU FOR YOUR HELP.