How often are we supposed to use fuel addatives? An indi-performance shop told me everytime I filled up with fuel, to use an addative. But one of my buddies who works on psd's all day long said those dudes from that shop were full of sh*t. My buddy told me every six months and it would be fine. I am in California, I know they use the ULTRA low sulfur fuel, I get my feul from chevron or 76. Also what is a good brand of addative?