not exactly sure for your year but there should be one near the firewall toward the middle it should have a yellow loop it its missing then there will be a black tube sticking out look near the egr valve in the back of the engine.
A Nissan 300ZX? No
On the underside, passenger side, of the transmission.
it is located on the transmission itself
If you stand in front of the driver's side front wheel, looking into the engine bay, it is right in front of you, slightly below the engine cover
Yes.
The "1990 Nissan 300ZX" was a very popular model in it's time. The "Card ID" website noted the carrying capacity of the "300ZX" was noted to be a hefty 1500 pounds.
http://www.zshop.net.au/Z32tech.htm
Yes my car is a 1990 300zx with a 2008 350z motor and 6speed transmission
226
Transmission fluid can be added through the transmission dipstick tube. You will need to use a funnel to limit spilling the fluid.
There is no dipstick on the standard transmission , the fluid level is checked at the fill plug on the transmission
wheel