I have a 5-Speed close ratio (i beleive) in my 240z.

Q: what is the correct oil to use for it?

the new stuff sold by Nissan is for the more modern trannys (very lite) but can i use it for this older trans?

Any suggestions

Read the FSM and use the specified weight/class oil. I use Redline.

Redline MTL worked great in my 280z with 82 5sp transmission.... but not great in my S2000.

Honda manual transmission fluid works great in the Honda and it is inexpensive.

My 4 speed has 235,000 miles on it, There is no record of a rebuild and I have every receipt that went into the car from new. I just refilled with 75-90 Purple and the damm thing shifts great and runs quite. Me likeeee this stuff.

I run Redline MT-90 in mine.

Really any gear oil works, but I ran SWEPCO 201 mixed with ATF 50/50 for faster shifting.

75-90 Royal Purple in mine. Works great hot or cold.

I run Redline MT-90 in mine.

Same here. The Redline made the shifting dramatically smoother.

You need a GL-4 oil, not a GL-5 oil. If you don't want to go synthetic, Pennzoil makes a non-synthetic oil that is supposed to be usable with "yellow metals" which should work. The synchronizers in the transmission are brass, and the sulfur that is in a GL-5 oil will make them brittle.

Last time I was looking, it seemed like non-synthetic GL-4 was tough to find. Fewer and fewer new cars use it anymore. Synthetics were a lot easier, for some reason. Numerous places had that on the shelf.

I'll also put in my vote for MT-90. Great drive train lubricant.

Redline.

I didn't know synthetic oil was bad for my transmission. I just changed the oil to synthetic. Should i change it again?