Do not put stop leak in it.
My family owned an automotive machine shop for decades and nothing good comes from that stuff.
Your symptoms sound so very classic head/gasket. You can lose compression between holes and take some coolant in the process. It can erode a channel in the block in a worst case scenario, but nothing that devcon won't cure.
Personally, I'd pull the head and assess the ridge and bore crosshatch before I condemned it. Grind and deck the head if the bore isn't chewed up....and roll for another 250k.