Leaky Petcock

[shawman]

I have a 2000 1500 Classic. Last saturday I pulled it out of the garage and when I turned the fuel valve on, gas stared coming out pretty good at the valve handle. I took it apart and inspected the rubber gasket and o-ring. they looked fine, but I ordered a rebuild kit anyways. This is my first time turning wrenches on my bike. I know it's a pretty simple procedure but
I want to cover all of my bases.

How come I didn't see any defects with the original o-ring? Should I coat the rubber with anything before install? My bikes only 9yrs old; is this normal?

I know I have quite a few questions but like I said, "covering my butt" As much knowledge as possible would be greatly appreciated.

Thank you, Shawman