We've had this discussion over and over in the SRT4 world. We even had a Chrysler engineer that had a hand in designing the 5 speed tranny for the NSRT chime in and he told us that as long as it was a high-ZDDP oil that it would be fine. Mobil1 syn oils that met the criteria were only the "high mileage" oils, specifically 10-40. The only other consideration is the coefficient of friction (the NSRT required friction modifier) so if guys are running their MANUAL transmissions already with syn without grinding then I would say that it is fine. It will not ruin any internals.

That said, the word manual is capitalized because this does not apply to the auto trans for the Crossfire. (my CYA statement heh).