I have always heard that you should stick with the same brand oil that has been run in a vehicle. I used to have an Isuzu trooper, when i switched from regular valvoline to synthetic, the engine would tick-tick-tick. Lifters i guess. I have used regular Valvoline non-syn oil since i've owned the cruiser (50,000 miles). Always been a fan of Valvoline, but wondering if it is o.k. to switch to full synthetic? Would it be beneficial or a waste of time? ???