From working at the Chevy dealer in the 90's I remember the fluid it called for was GM synchromesh manual trans fluid. Gotta get it at the dealer.
the T5 manual I have says to use Dexron II ATF.....it also says "do not use gear oil as it will damage blocking ring material"
Synchromesh is the viscosity of ATF but had friction modifiers similar to what Honda put into their auto trans fluid. You can put atf in the t5 with no problem. But once you use atf stay with atf. you don't want to drain and refill with the synchromesh fluid. They don't play well together.
I like the Ford SP oil in the t5. Made my Mustang shift way better so I put it in the Coupe as well. It's a GM T5 WC. I am sure LV would be good as well but it stinks.
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