If I'm a Diamond Member and the preferred parking lot is full can I park on the general parking lot for free? or I need to pay for that still?

Still free

As long as you are a member (diamond or otherwise you are free to park wherever you want to. If preferred parking is full, then they will get you the closest possible spot to preferred area.

If you are a diamond member they will find you a parking. It's all about the business!!

Free. But it's so far away!

You are still free