I know that base oils aren't the end-all, and that most oils are a blend of base oils...but are di-esters used as basestocks at all anymore? You hear about PAO's and Poly-ol Esters being used, and obviously group 3's, but no diesters. Back in the early days of syn oils they were the be-all and end-all of base oils - excellent in the cold, held viscosity perfectly, cleaned engines, and had low volatility. Are they still around in engine oils, or are they just not used at all? You just never hear about them being used! I know they are expensive to use, but with formulators looking for every edge, you'd think someone would bring them back into the mix, no?