[redranger]

I'm no expert, but I think your mechanic has it wrong. Everything I've read and been told by experienced p-car mechanics is that synthetic is not supposed to be used in the 915 gear boxes. Swepco is the brand to use for 915s. Synthetic gear oil is reserved strictly for the g-50 boxes.

I've got a short shift in my 911 and I use swepco, no issues 102k miles...knock on wood