No error codes in the tcu or ecu whatsoever. I think it's definetly a contact fault.

I have the ZF manual for the geatbox, only if my german was a bit better..

I have an idea that maybe the 4th gear solenoid is actived trough 2 different circuits depending on wheter the probram switch is on M or S/E. Though I haven't confirmed this yet..

Advices are welcome..