I have used Valvoline conventional for years in my cars with no problems. After I bought an 02 Infiniti I35, I switched to Valvoline Duroblend after about a year. I then read here that most blends contain less than 50% synthetic, maybe as low as 30%. Also seeing that some people are constantly switching back and forth beween syn & conventional, I decided to try my own blend. I "blend" 50% Valvoline conventional 5-30 + 50% Valvoline full synthetic 5-30. I think this is cheaper than the Durablend, and I now have 50% synthetic. Any comments?