HI, I want to buy a gas cap for my mini, but I'm kinda confused... Do I need to buy a Dummy Tank Neck (it's Right Hand but I can't find a Left Hand, will it fit a Left Hand tank too?) for this Gas/Petrol Cap? Oh, With the gas cap it mentions that's it's held on by grub screws, but where do you screw them? Is this the type of thing that will make sense, once it's in front of me?...