That "Screw Plug" has an o-ring on it. On the older ones the o-ring would kinda disintegrate. A hardware store o-ring was a worthy upgrade.If it keeps leaking replace em.CJ
I don't know what purpose a plug under a plug would be but there is no extra plugs on my G5.The hex under the plug on mine is for unscrewing the fork tube from the upper tree.CJ
There is no plug under the slotted chrome top plug on the G5. At least not on my G5. I have previously removed the chrome plug to check the fork oil level with a wire dip stick - only one plug to remove.