Where do you add transmission fluid to a 1991 Nissan Stanza with a manual transmission?

The plug should be on the side of the transmission facing the front of the car. It will be just like an oil plug only you will need a suction gun to get the fluid in the hole make sure the fluid is at the right level before driving fill it till it starts coming out the hole then let it settle for 15 20 minutes top off and then check the dip stick. Please be aware that 'Transmission Fluid' in a manual transmission is actually called 'gear oil', and is a different substance with a different purpose. Transmission fluid in an automatic transmission *is* a lubricant, but also serves a hydraulic role, which means that it is pressurized and used to move various parts in the transmission. The gear oil found in manual transmissions is simply a lubricant intended to extend the life of the moving parts inside a manual transmission. Please, NEVER, NEVER use manual gear oil in an automatic transmission. Automatic Transmission fluid will have Words like 'Dexron', 'Mercon', or 'Type F', and is usually a pinkish red color, while Manual Transmission oil will be called 'gear oil' or '90 weight' (maybe not '90' but something thick like that) and be a dark color. If you have a rear- or all-wheel drive vehicle, please note that your differential(s) (the part that transfers driveshaft power to the axle) will have gear oil in it/them, too. The final difference is the duty cycle: automatic transmission fluid should usually be changed more often than gear oil.

ATF has a GL-4 rating and as such is actually suitable for quite a number of manual transmissions, especially in Japanese cars. It is the specified oil for some. Using an oil that is too 'heavy' or 'thick' for the transmission or the temperature will not improve the reliability of the transmission. Instead it will cause damage by preventing the synchromesh from working. Baulky synchromesh, especially when cold, will often be cured by draining 50% of the gear oil and replacing with ATF. ATF has a viscosity similar to an 80W or 75W-90 gear oil and can be used in any manual transmission where a GL-4 oil of this viscosity is approved. But it is NOT a hypoid oil (GL-5), so can't be used in hypoid manual transmissions such as Subaru. Bottom line: check your vehicle owners manual for lubricant specifications and servicing schedule. I'll post the specs for a 1990-1992 Nissan Stanza here shortly...