Transmission Faut

i had also same fault message about transmission it is operate in one gear
and when i send the car to transmissions technician and he said to me the
fault in the valve body you must change it and t is very expensive to change
to new one
when i search on internet i find a same valve body but manufactured in
china i don't know about the quality of this valves
please advice me if you have a solution or if you know some dealers on
internet have a used re-manufactured valve bodies
and i want to know if this is the main reason of this fault
my car is : BMW 525i e60 2005
the valve body model is : ZF6HP26