Hi keetz & welcome to the forum.

Perhaps you can tell us a little more & you might start by adding a basic location to your profile so that we know which country you are in.

Who repaired the gearbox & what do you mean by 'weak parts'?
Not sure what you mean when you say that it is difficult to 'turn on' the second gear. Is it stiff or tight to select second gear, or does it crunch when going in, or does it go in but not want to come out?

A bit more detail will go a long way towards us being able to help.
So welcome aboard & if you can help us to help you, then the world will be a better place.