The thing with asking for things through Visualization and the other techniques represented in "The Secret", is that it has to be asked with precision. And the more precise and specific you are about what you request, the easier and faster it will manifest for you.
In your instance, you got your new car, just as you asked for. But you never specified (or so it seems) that it would be your car from now on. That it will be fully yours, and yours alone. So you got what you asked for, even tho it was temporary.

Any way, I love reading these manifestation experiences. It surely helps me with my own faith in these techniques. And yours is highly detailed, high quality post. Just perfect.

Also, you can give Neville Goddard teachings a go. I find them clearer and more straight to the point than The Secret. You could start here: Consciousness Is the Only Reality if interested.

Thanks a lot for sharing this story with us friend @YouAreYourOwnGod! It surely helps everyone of us to switch from a materialistic perspective on life to a Spiritual Perspective on Life.