Mueller Elite Masticating Slow Fruit/Vegetable Wheatgrass Juicer

I'm mostly interested in juicing leafy greens (spinach, kale, etc). Does this work well for them?

The instructions don't show where the rubber ring goes, can someone please tell me?

How long would it take to juice an ounce of wheatgrass? Also, does it extract a good amount, leaving the grass almost dry?

Does it work with wheatgrass?