Suspected head gasket issue
 

Need some really creative ideas here, everyone. My 96 F150 302 cu. in. with
170K miles has been leaking oil into the coolant. Not a huge amount, but enough to turn the coolant milky and scummy. I've replaced the coolant once to clean things up, but the condition returned right away. I've tried several bottles of Wynn's Engine Oil Stop Leak with no success. The engine purrs like a pussycat, so I really don't suspect a cracked head. I know that pulling the heads to replace the gaskets will be a bodacious job because the nuts and bolts are rusted into place. Wouldn't be quite so bad if it is possible to narrow down the issue to a specific head. Sure would cut down the cost of repairs. Anyone? Many thanks!