Damage around screw holes seems a common issue on Tamiya cars. It could have occurred due to a combination of factors. Screw holes create points of stress concentration in the chassis. When a screw is tightened, the material around the hole experiences higher stress than other areas of the chassis. In fact, sharp edges and corners around screw holes can act as stress risers, where cracks can initiate and propagate under load or vibration. AND, when screws are tightened, especially metal screws in plastic parts, heat can be generated due to friction. This heat can cause local expansion of the material, followed by contraction when it cools down, potentially leading to cracking.
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