How common is Gen 2 Head Gasket Failure after 300,000 miles?

I'll simplify the question: The only places where coolant can enter oil are:

1) Head gasket

2) Timing chain cover (RTV seal or damaged cover).

3) Pipe plug in head.

4) Crack/hole in head.

5) Crack/hole in block.

Surely someone here can confirm or dispute.
I'm 99.9% sure, but the reason I am asking is to avoid that "Do'h! All this time it was actually leaking at the ____________!" moment.

 

You sound like a smart guy, but post some odd replies, at leat from time to time, in this case completely missing the question.

The question is: Are the paths/interfaces listed the only places on a gen 2 prius where coolant can theoretically enter the oil?
I think they are. There is no oil cooler in the radiator, for example.

 

Surely many here know?
Are these the only places on a (Gen 2) prius where coolant and oil can mix?

1) Head gasket

2) Timing chain cover (RTV seal or damaged cover).

3) Pipe plug in head (10mm hex key).

4) Crack/hole in head.

5) Crack/hole in block.

 

Come on now, this isn't supposed to be a hard question. And NO, I'm not looking to "ambush" anyone by bringing up possibility 6) after they say "that's all of them".
The reason I'm asking is that if there is possibility 6), I of course want to look into 6) before I take the head off again.
Makes sense, right?
I don't think that there is a 6), but I would love to be wrong...

 

It's purely a theoretical question (not about my specific sample) just to confirm that the "list of 5" contains all the areas where oil and coolant mixing on a Gen 2 COULD happen.
I'm pretty sure the list has them all because there is no oil cooler in the radiator, for example.

 

Out of curiosity, has anyone for example heard a story of someone replacing the head gasket only to find out that the pipe plug in the head had been leaking? (I'm certain that this is not the case with my car and I believe that this potential failure mode on an engine last assembled by the factory is extremely rare and on engines that have been worked on by someone is also very rare, barring cases of some kind of mistake or miscommunication (shop opened it while cleaning the head and for some odd reason didn't tighten it or even put it back and customer didn't realize it's even there or didn't expect it to not be tight and didn't check).