Leaky master cylinder

Check the sealing surface on the top of the MC. They are not always perfectly smooth. If it has a small grove or imperfection, that is where it will leak. If this is the case, take the MC back, and get one that is smooth.Do Not use any kind of glue or sealant on your gasket. The brake fluid will eat it up, with the possibility of it getting in the system. You could also try a new gasket or lower the brake fluid a little.