One of the questions I get a lot is “can I add some stop leak”
I have never found anything in a bottle that will resolve what happens to a Subaru Head gasket. I took some pictures from a Subaru Outback in the shop today that had some stop leak put in, only to over heat the next day. The cooling system is just full of this stuff and it really did no good as seen in the pictures below.
I really have never found anything that will permanently resolve a head gasket leak on a Subaru. While I truly understand the displeasure there can be at the though t of a repair like head gaskets, I do also want to warn that adding stop leak can add to the cost of the repair.