Can you run synthetic oil in the rear end and transmission(I think you can but just checking). Is there any advantages in it. any problems you have had.

 

Yes

 

I just installed NEO 75W-90 RHD in the newly rebuilt Miata geared transmission.

Not really satisfied with the noise in 4th gear, Considering/thinking about changing to 80W-140 EP

 

The transmission is smoother as a result of the new fluid. If that's because it's synthetic I don't know for sure. It seems happier in the cold switching from 80W90 to 75W90. It doesn't seem to get as hot either, but that's not exactly a scientific analysis.

 

Yes

Better efficiency, lower operating temperature, superior stability, reduced transmission shifter "notchiness", and it works great in both very hot and very cold weather. Unlike synthetic engine oil, it is actually worth paying the extra money for synthetic gear oil for your street car.

Yes, it works so well that I now refuse to buy petroleum gear oil. This is a problem because synthetic gear oil isn't available at most auto parts stores, so I spend a lot of time calling/driving around town trying to find it, or I have to order it in advance via mail.

I like Red Line MT-90 in the transmission, and 75w90 in the differential.
http://www.redlineoil.com/

Other good synthetic oils:
http://www.amsoil.com/
http://www.neosyntheticoil.com/
http://www.royalpurple.com/

Synthetic wheel bearing grease is also excellent. I have used Mobil 1 for many years with good results, but the brands listed above also make synthetic wheel bearing grease. Just a few days ago I picked up a tube of Royal Purple grease to try out.

 

Used RedLine in both. Tranny seemed a little slicker shifting. You'll probably notice a big difference if you drive in cold weather.

 

I used to have a grind down and up shifting into 2nd gear.. I switched to Redline MT-90 (bought it at summit racing, like 30 mins from my house) and the grind has ever since been gone.