Mazda fixing a problem with lock tight

I complained about my gearbox on my brand new vehicle, which Ben Morgenrood Randfontein where I bought the vehicle had to replace after 16 000km. After installing the new gearbox my vehicle went into reverse instead of 1st gear, I took it back and the reset the linkages on the gearbox. 2-3 Months later as I was on my way back from Potchefstroom to Randfontein I had no gears as my selector box dropped, my friend helped me to get back home only to find out the bolt on the selector box fell out. So after replacing it we forget that we replaced it and after almost another month we had the same problem we took the vehicle to Ben Morgenrood where the bolt got replaced by their service department. So in December we went to Cape Town with no problems but then in January the same problem happen again on our way from my son's grade 8 play in Krugersdorp and we a friends child in the vehicle to drop her at home. I took the vehicle back and the replaced the bolt and only put on lock tight to fix the problem. I sent Mazda SA a; mail on this problem which they only rep**** to say that they are satisfied and lock tight was the correct way of fixing the problem. I am not very satisfied with this.