The GM and Chrysler synchromesh gear oils are very light gear oils ... formulated specifically for synchronized manual transmissions (tuned to have the right coefficient of friction). They are about 9.0-9.5 cSt in weight @ 100 degrees. But these dealer-fluids are NOT the only game in town.
The cheapest replacement would be to get Pennzoil Syncromesh which is a replacement formula found in many of the big-box auto supply retailers:
http://www.pennzoil.com/products/gea...cro_fluid.html
Or Honda MTF:
http://www.manchestermotorsports.com/index.cfm?pid=210
Me? My next change on my '06 Honda Civic is gonna be Amsoil MTF, I think:
http://www.amsoil.com/storefront/mtf.aspx