I agree that the synthetic oil is not the issue it used to be when it was first introduced.

I had a mechanic tell me once that he ripped apart a motor at 60k, because it never developed the power it should. When he took it apart, he could see all the machined lines on the cylinders that showed it had no wear whatsoever, not enough for the rings to seal. They ran regular oil for a few thousand miles, until the power developed, then switched back to synthetic.

That was in the early days of synthetic and I believe that issue has been resolved, if it wasn't, you would hear more about it, and it would be documented in the manual. I'm guessing most of us run synthetic in our G's. This may have been good information in 1990, but I think it's outdated now.