Slow day. So I'm talking to myself. Nothing unusual about that.
I think I've got this sorted out. The manual appears wrong, or else they changed it for this year. Or maybe they just have a lousy artist!
When I went back to look at it again, I see that the tube that's leaking is the overflow tube which runs to the side of the filler cap area. That looks different than what's shown in my manual which shows them the other way around. Hence the concern.
Assuming the tank ventilation is intact, which looks like it's the tube that vents through the back of the back of the cap, I think I'll be okay just capping off the overflow one.
I've been through ventilation starvation before (CA gas cap on a 49 state tank) and don't want to repeat that experience.
If you're still reading and want to confirm this, feel free. I only have myself to discuss this with. :)