Originally Posted by SloopJohnB@mac.com
I add, ZF the trans maker says do it 30-50k miles depending on severity of usage.
Actually what I found from ZF is 50K to 75K miles or 8 years.
One reference said 50K to 75K if used in severe conditions and lifetime if not.
Other said 50K to 75K in normal and more often is severe.
Nothing from ZF suggests not changing the fluid if it has gone over that.
I sent ZF technical service the question.
It will be interesting to see if/how they answer.
Just found out, ZF services North America is only 20 minuets away.