There are two plugs on the 300zx manual transmission. on on the passenger side and one on the bottom of the transmission. You can unscrew them with a 1/2 drive ratched. fill through the plug on the side, drain from the plug on the bottom
The FSM calls for a 'Dexron' type transmission fluid.
Yes my car is a 1990 300zx with a 2008 350z motor and 6speed transmission
Automatic Transmission fluid
75W-90 GL-4. Redline MT-90 is the best but, you can use whatever you want
In the transmission.
You put the Transmission Fluid in the Transmission (fill point transmission drip stick tube)
The transmission will fail.
Into the power steering reservoir under the hood.
Low Transmission fluid
The power steering fluid reservoir is up on the passenger side wheel well in the engine bay. Looks like a short fat silver coke can with hoses coming out of it. On a side note, the 300zx twin turbo uses ATF (automatic transmission fluid) not power steering fluid. usually a green casing with black top. the following link is NOT a 300zx, but the reservoir is about the same. http://www.sillbeer.com/images/engine/power-steering-reservoir.jpg
Buy a transmission funnel and pour the fluid in the dipstick tube.
In the transmission!