2004 Sienna headgasket leaking.

[Trav]

It is and GM is repackaged Bar Leak tabs, they work well and cause no issues.

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Amazon.com: Bar's Leaks HDC Radiator Stop Leak Tablet - 60 Grams: Automotive

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[Gasbuggy]

Subaru coolant conditioner is rebranded Holts IIRC

Yes, but these products are mostly just marked up sodium silicate.

 

[Trav]

The Subaru, Gm and Bars are ginger root based and very effective without clogging.