Reverse speed not working anymore (started by sliping)

Hi please can someone help me with the tranny technical document? I have a 2006 FX35 the reverse speed started by slipping but now it is not going back anymore but the five speed are quite good and working normally.
Or may be there is a solution that you can tell me to do?

I recently opened the valves' module and find out one of them which is different from others is not blocking the air on one way as it should. But don't know if it's the real problem. should I change the valves kit ou anyother action to be carried out.

I'm completely desperated now spent so much money on that car and still not working. my email : [email protected]
from Central Africa - CAMEROON