RPM fluctations

[mcs]

Check the plastic tube on the top of the pan for leaks where the wiring harness goes in. This sleeve seal is common for all ZF leaks. In addition, you may want to order the 4 rubber tube seals and the bridge seal and have them changed when you service the box. These seals can leak fluid internally and cause the gearbox some issues

The sleeve seal leaks externally and the ZF box doesn’t enjoy low fluid at all.

The ZF 6HP26 is capable of operating the solenoids to overcome internal and external fluid leaks and therefore pressure changes. So once repaired, simply reset the adaptation for the solenoids.

Google ZF 6HP26 seal and it will come up with many things. Otherwise these boxes are pretty bulletproof