The ZF trans, like the ZF trans in Audi ARE considered non-serviceable by the auto manufactures that use them in their vehicles. As the service manager,
@Podcast is not wrong.
The trans manufacture has a listed a service interval, but that is with the understanding that the service is done at their specifications (which is very unlikely). These transmissions are so sensitive to fluid levels, one takes a big risk by servicing it. If done correctly, there is no issue, if even slightly off, say goodbye to the trans.
I have 130k/15 years (unserviced) in the NY Metroplex on my A4's ZF transmission. Not a hint of any issues at all.
I have yet to hear of a ZF trans failure because of a lack of service. Every failure I've heard of was 1) a flaw from the factory or 2) a flaw from improper service. Their trans is very sensitive to any impurities, apparently there was an issue with some impurities getting in at the factory.
The proper service for my Audi requires getting the transmission level (which is not the same as getting the vehicle level), and using the trans temp (using the VAGCOM software) to test the refilled level. If the temp is too low, the temp goes too high, in which case, you have to leave the vehicle with the trans level and let the temp drop back to a certain resting temp. This resting temp is really only achieved by leaving the vehicle on stands overnight in a temperature controlled garage (winter temps will affect fluid levels).