Is the remaining amount from accident compensation, after repairing the car, which was used for other car repairs not resulting from the accident, permissible or impermissible (halal or haram)?

If the amount taken by the questioner covers the damages to his car, then he is permitted to take and own it, whether he repairs the car or not, or repairs it outside the dealership to save costs. The amount is his property, and he may do with it as he wishes, bearing in mind that the value of the damage is not estimated by repair costs alone, but also includes the depreciation of the car's value due to the accident.