FWIW, this has been widely debated in other forums. A couple have used synthetic fluid, but it is really not recommended, and has never been extensively tested. The GM supercharger fluid is apparently used because of it's ability to not foam and cavitate when running at 15k+ RPMS. Synthetic engine oil does not have these same properties and the cavitation can cause excessive wear problems on your gears. I understand you wanted to change the fluid, but I would try to get the correct fluid in there ASAP before too much damage is done.