My local Nissan dealer told me that they do not recommend using synthetic oil in the manual transmission. They say that because it is so slippery the syncro's cannot function properly which can lead to gear damage.

 

Not exactally true. Both types can be. Synthets formulkated for the application are not. It IS TRUE gear can be too slippery for proper syncro engagement. I would imagine synthetics woulod exagerate this. I use Redline MTL (in my other car, a 5-speed(my Max is an automatic)) and its great! Redline explains it on their web site. See:

http://www.redlineoil.com/whyredline.htm