Any recommendations ?
The car will ( one day ! ) be used for sprints and track days etc.
Many thanks

 

Its normal to use ATF (automatic transmssion fluid) Around 2.5 litres

 

Many thanks.

 

Don't use normal ATF, the nearest fluid made these days is a atf, but a specific one, it is CASTROL TQ-D, halfords sell this.
Interestingly a different oil is specified for WC and NWC boxes, NWC being a 70 weight gear oil, while the WC uses a ATF, was dexron 2, but no longer made, mercon was ok to use, but again no more, castro, tq-d is the closest, using the wrong stuff will screw up the blocking rings.
tabetha

 

bara motorsport recomended 75/90 synthetic in mine.. its a little stiff to engage when cold but fine after a few miles.. the bix i have at the mo has lasted a lot longer than some of my others which i ran the std stuff.. used to get quite noisy after a few hard blasts..

 

we actualy just went through this with my cossie not to long back, had tabetha and I doing a bit research. Our T5s are WC T5s and use fibre or almost carboard components on the syncros, the ATF stops these parts from being damaged or prematurely worn out.

I was running standard gear oil in my tranny to start out with but found it shifted horribly.. once I swapped it out for ATF the difference was night and day.. So smooth even when it was cold!

What I ended up using was Delco Dex 6, it is compatible with Dex 2 and mercon, and what we use at GM in all the WC T5 cars.

 

The problem is the amount of variations of the T5, if you counted every possible combo it would likely be well over 1,000 different specs and that isn't even counting the T5 Z, or Z spec as the us call it.
There is a way to tell the box apart externally whether it is a WC or NWC, but only if you can see the front of the box hidden by the bell housing, the bearing race closest to the input shaft is indented on a WC and flush on a NWC.
WC and NWC have NOTHING to do with power potential either, WC is world class, simply meaning same box(spec) used all over the world, NWC meaning variants of base box used all over the world.
Later T5's actually had electronic speedo drive, one is on it's way, with the addition of a sleeve to make up for a 6mm difference in diameter will fit cossie T5's.
There is a multitude of different materials used, and to make matters worse, what is supposed to be in your cossie box isn't necessarily what's really is in it!!
tabetha

 

I used this on mine a couple of weeks back and cold gear changes are alot smoother.

 

TORCO 75W/90 all the time,one of the best gearbox oil imo.