Notice that when playing now with 4x4 the "mother****er" did not turn...Now i understand why the last owner wanted to sell.
So:
-It was the pinion on the servo motor that was way lose. I could glue it... but i had a miniz servo motor which have triple the torque and a metal pinion so once opening it do it right the first time!
-Some second hand things always have an hidden "mouse" somewhere!! It's up to the new owner check it, and fix it! Otherwise sell it! lol