What brand of transmission oil should I use for my manual rx7?

 

Any brand that meets the specifications laid out in the Factory Service Manual. See the FAQs for links to the FSMs.

For the record, I use Amsoil Synthetic.

 

Since the FSMs usually specify a GL-4 in 75w-90, I use and recommend a synthetic GL-4 such as MT-90 or Amsoil MTG. While many GL-5s will work there is always a question of ideal synchro performance and corrosion of yellow metals. So it's worth it to take an extra minute and buy the exactly ideal fluid.

In the differential I use a more gearing-focused gear oil like Redine Lightweight Shockproof.