I'd definately stay away from the
oil treatments. The product may be wonderful, but think of it this way; you should be trying to solve or prevent a problem. What problem do you have when using the syncromesh? BTW, here is a link to a product description of the stuff...
http://www.pennzoil-quakerstate.com/...omeshFluid.PDF
By adding an
oil additive, you may be causing more problems than you are fixing. You can alter the viscosity index, the EHD lube film (acronym for a long word that basically means the lube film thickness between the gearing or bearing elements), and other factors. It looks like the product is meant to improve the friction coefficient to provide better shifting. Again, only use stuff like this to solve a problem.
The most important function of the
oil in a gearbox is to keep the metal parts from touching each other. Sometimes this is done with additives at the manufacturer (EP oils), or aftermarket additives (slick 50, STP, etc.). I design, and the company I work for manufactures gearboxes for industrial equipment up to 2000 hp and high speed boxes up to 50,000 rpm and we never use an aftermarket additive, and almost never use an EP oil. The critical factors are viscosity, and viscosity index.
Other than the pain in the rear of getting oil in and out of the transmission, oil changes on a manual trans are fairly painless. As already mentioned, the higher plug (generally near centerline) is the fill, the bottom is a drain. Fill until the oil comes out of the plug hole. The PDF manual that you indicated has a 3 qt capacity listed on pg 44.