Transmission issue 8HP70X

[Pruzina]

2011 X5 50i (150k)
8HP70X

DTC
4EC8 - Position sensor
4EC9 - Parking lock
4E98 - Transmission ratio monitoring, clutches A, B and D

Here are the exact symptoms:
When cold throws 4EC8 (position sensor) car drives forward and backwards and possible engage Park

After couple minutes D and R not engaging shifts in N (N is flashing) unable to shift in to P

Checked tranny fluid and is full but the fluid is really really dark and the filling plug was almost impossible to loose so clearly fluid never changed.

First thing what I'm about to try is to change the fluid and filter but I'm not expecting that it will solve the problem.

Seems like pressure issue. once the fluid warms a little won't shift.

Does anyone know if it's worth to do valvebody rebuild and solenoids?
Really don't want to spend money on rebuilt and solenoid kit just to find out that the internals of the tranny are shot. I rather skip that part and get another trans.