Proper T5 trans fluid
 

I know it uses auto matic fluid, but which spec? dextron? mercon? I want to run a synthetic.

It uses Mercon III/Dexron

I put Mercon V in mine (which is synthetic) and it works great.

Are all mercon V oils synthetic? Thats what my f150 uses. I just bought some for my truck, Castrol, and it says it is part synthetic.

I've been using Red Line manual trans. fluid for the past 3 years in my T5. I change it about every 5000miles. I also put in a container of automatic trans. treatment from Prolong in it with the Red Line. I run 2.5 quarts of Red Line and 1 container of Prolong automatic trans. treatment. This stuff work great. It makes the trans. really smooth when shifting. The Prolong can be found at PepBoy's.