Fixing head gasket leak with a sealant?

Can a small head gasket leak be repaired with a sealant?

A friend had it work for him. He had a misfire code and it would not go away no matter what he tried. The truck ran fine, but if he turned it off, he had to reset the code before it would start. The mechanic put in an additive and it cost $90. I don’t know what he used, but it fixed his problem. I would assume all work on the same principal. When exposed to hot gasses they harden and seal the leak. Hopefully someone can point you to a brand.
I found this one that is supposed to be good.

I would try a sealant only if the car is not worth the cost of a head gasket replacement.

Here’s a link to a previous discussion on this same question.

Look closely at @tester’s recommendation on sodium silicate.
But I agree with oldtimer11. Use sealant only if the car isn’t worth the cost of replacing the head gasket.