I found this when I was looking for info on the ZF 6HP26 transmission. It's actually a Ford document, but it goes into a lot of detail explaining the workings of the transmission which is used in Lincoln Navigators as well as the 2003+ XK8s. The good stuff starts on page 3-40

http://www.motorcraftservice.com/vdi...es/30n29f0.pdf

 

Looks like (per page 3-50) to replace the fluid you drain, remove the pan, replace the pan with a new one, replace the pan and fill. You have to replace the pan because the transmission fluid pan, gasket and filter is a one-piece assembly. Is this the only "maintenance" you can do to the trans? I wonder how many miles it makes sense to do it?

Reading about all the controls, solenoids, etc. - this is really a complex piece. Remarkable that it is a reliable as it is. Good thing too.

Jack