[Blas]

You are not using one of those Mr. Gasket chrome thermo housings are you? I remember hearing horror stories from people about them.
You said in one of your repair attempt descriptions that it leaked even without starting the engine.... so system was not hot or pressurized and still dripped....
I'm liking the long bolt possibility scenario... you could remove the housing and just replace the bolt to see how far it threads into the manifold as a quick check. Not the issue if it bottoms out or the bottom of the bolt head is visually lower the thermo housing flange thickness. Could also go with stud and nut to replace bolts. where exactly id the leak emulating from? Grab a cheapie replacement housing from an autoparts store and fit it to see if the problem persists.
Blas