ZF 8 and 9 speeds use the same fluid. ZF (depending on where you read it, it varies) recommends service between 40 and 60 thousand miles, or 100,000 km. Fill for life (Chrysler's term) means to me when the trans fails, that's life, c'mon in for a new car. So we're spending the bucks on 50,000 mile service intervals. My local dealer only does flushes, my transmission guy says, no way, so we change the pan (integral filter) and fluid, no flushes for us.

The German top manufacturer of transmission ZF recommends oil change every 8 years or 100,000 km. The oil change interval is actually set by the type of the transmission and also by the strength, or how long it is designed to be.