Best engine oil stop leak

Unless you plan on rebuilding that engine very soon none. That stuff works temporary or not at all and for a very short time. Think about some chemical goop circulating through your engine looking for holes to plug. The rod bearing oil holes... and so on. And you say very bad..it's not going to work. Sorry. There are some guys that might disagree, but I stand by what I said. know, the label makes fantastic claims. But its bull

Are you sure it's not valve cover gasket? That's an easy and cheap repair

As above, I would check valve cover gasket before poring stop leak in the engine.

Stop leak is useless on a cork gasket, it will actually make it worse. Just replace gaskets