I am one behind. I have seen it six times. And the six time was the best! It gets better every time I see it.
As for the car - I have seen it. It is on a wide shot at the corn field scene, and is moving quickly. It is right after the chimney smoke. You can only see a dust cloud moving quickly, and not what is causing it. I think it is black riders on the road, because a car would not have been unnoticed or ignored in editing, I think.
I had not heard about gollum at the Argonath... The object in the eye is a bird's nest I think. Gollum would not be out in the sun like that, IMHO.
As for the books, as it turns out, Gandalf is alive! Merry and Pippen are fine, and all of the Fellowship survived a hard battle at Helm's Deep. Saruman's place is a mess and he is fit to be tied. Still no word from Sam and Frodo and I am quite worried.