Very nice work on the Pantera, Aki!
As for the flex in the chassis: you do not want flex between the gears, the part between the rear axle bushings and the motor should be as rigid as possible, otherwise the gears will not run smooth while flexing.
i like what you did to the wheels - they look great!
the photo with the chassis in the box is great!
the details are very nice, very crisp! i like the exhausts.