[Aredubjay]

The first thing to check is that your PCV valve is operating correctly. It's a pain in the butt to get to, but, that's the first thing to check.

Otherwise, yes, it's the little o-ring on the dipstick (from experience). I busted mine trying to take it off to find an o-ring in my box-o-goodies of things in my garage. Couldn't find one. "I'm screwed" I thought. Then, I noticed that fuel line is about the same circumfrence as the o-ring. I sliced off a piece of fuel hose of the same width as the notch in the dipstick and rolled it into place. I nearly have to get into the engine bay and pry the thing out now. Working like a charm now for more than 10K miles.