It is normal to have some mechanical issues.
Art2 is one of the points where you can find that gear do not fix. To solve this problem we have build a 3-4mm wedge in Art1body. This way gear of the motor2&3 fix better. I will send you an image as soon as i can for me to make myself understood.
However we do not have problems with Art3 and Art4, We have problems with art5&6, the diferencial.