stock GetNearestVehicle(playerid, Float:dis)
{
    new Float:X, Float:Y, Float:Z;
    if(GetPlayerPos(playerid, X, Y, Z))
    {
        new vehicleid = INVALID_VEHICLE_ID;
        for(new v, Float:temp, Float:VX, Float:VY, Float:VZ; v != MAX_VEHICLES; v++)
        {
            if(GetVehiclePos(v, VX, VY, VZ))
            {
                VX -= X, VY -= Y, VZ -= Z;
                temp = VX * VX + VY * VY + VZ * VZ;
                if(temp < dis) dis = temp, vehicleid = v;
            }
        }
        dis = floatpower(dis, 0.5);
        return vehicleid;
    }
    return INVALID_VEHICLE_ID;
}

CMD:repairveh(playerid,params[])
{
new nearest = GetNearestVehicle(playerid, 10.0);
RepairVehicle(nearest);
SendClientMessage(playerid,-1,"Vehicle Repaired");
}