Transmission fault
 

I bought a second handed range rover L322 year 2003.
After a month, my transmission fault and have to overhaul.
After overhaul,the mechanic told me still got some problem.
Thus,i have test drive the car, it moving normal and suddenly check light came out become no power.
I ask another mechanic to help me diagnose, it shows gear monitoring 2 fault.
So,i want my money back from the mechanic, but he said it is ecu problem not his fault.
Is it real? Or he just dont want to take the responsible?

i Also have had to replace tranny, little did i know 2003-2004 used BMW . Reverse still a problem . have to let it engage fully before touching gas or it will do the clunk and jerk. Always a strange sound