You don‘t need a polarizer if you have an OCF and a softbox… or multiple. If you are trying for proper car photography this should be easy to get.
The setup will be crucial.
- find the right angle you want to take the picture from.
- place the camera and do not move it until you’re done.
- take a picture.
- place the flash at an angle the will not reflect into your camera. The more flashes you have the better.
- take a picture
- repeat at step forciert a different position until you have properly lit the whole car.
-> go into Photoshop and stack all your images. Mask out the highlights you have created and blend everything together. Done.