My friend, I'm sorry to say that particular model car is condemned by the so called zinc pest! This phenomenon is also known as Zamak cancer and it's caused by a chemical contamination in zamak, which is a metallic alloy diecast model cars are made of.
When such phenomenon happens, the affected parts tend to expand and crack in an irreversible process and there's absolutely nothing we can do about it, but look for a new model car to replace the damaged one!
Zinc pest is our greatest nightmare, since it can affect about any diecast model car from any brand, no matter whether it's a cheaper or a premium one! And, as it takes place, the metal starts "rotting" and becoming extremely brittle, at the point it simply starts cracking and falling apart! Some model train collectors tried, without success, to dip the affected parts in vinegar. The process had been slowed down, but that was it, as parts continued deteriorating! Very moist environments also tend to lead to such processes, but, fortunately, that is not a rule, since not all model cars kept in the same condition tend to have such problem!
Thus, whenever you see such cracks on a model car model, pray they exist only on some moving parts, since those can be replaced if the car body is intact. In case the body is affected, it will be just a matter of time for the model car to be about gone and become a donor of the non affected zamak parts, as well as the other "non-zamak" parts.
That's sad, but true!
