Indeed, but the hidden hole has the same bore as the head bleed pipes and is permanently open. There's no reason why it should block there than anywhere else in the line. In fact from all the reports I've read, this hole has coolant flowing through continuously with the V6. When the cap's in place, the much smaller neck drilling is permanently closed and stagnant. A dead end for debris to accumulate, which it does pretty often.
TC
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