2004 Sienna headgasket leaking.

[Trav]

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

https://www.amazon.com/Genuine-GM-1...21dec&pd_rd_wg=kEiN7&pd_rd_i=B000QIH3C4&psc=1

https://www.amazon.com/Bars-Leaks-H...0f5cf&pd_rd_wg=XY6Ze&pd_rd_i=B000KKND3Q&psc=1

 

[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.