Gearbox Oil & Idle Issue

[scitzz]

I used to use ATF, but changed it to 80w90... i don't know, it sounds and shifts smother. but i believe is a personal choice, both work!

Yep. Me, I could care less about noise, as long as that puppy works

Aspire had the same trans with a taller final gear, person up ^there is correct!

[Bert]

In the Festy manual (93, anyway) it says to use Mercon ATF in manual trannys. It's a bit of a bugger to refill through the speedo drive unit hole. And you're not supposed to overfill either.
These cars are long ago off warranty so whatever you want to try in a tranny is your business. Down your way there is a highly rated synthetic tranny oil called Royal Purple. Consumer Reports (or one of those agencies) testing found it to beat all.