Thermostat was bad, overheating then a bad leak at the housing. Stripped lower thermostat bold. We tap a bolt size bigger and get a tight fit on the housing, but still a leak. Even added plenty of RTV, still a slow leak.

Any chance the housing from the radiator hose is slightly warped? Why would silicone not seal this thing?

Or is this a hairline crack in the intake manifold at the thermostat? Can't see one.

Thanks for any help.

I would take a closer look at the housing , especially if it was not leaking before.
Use a straight edge to check the sealing surface for flatness. Take a really close look for any sign of cracks, replace if the housing if the surface that seals onto the manifold looks pitted . Make sure the thermostat was installed in it's proper spot and not jammed under the housing sealing surface so as to create a gap and then leak.

Ford's thermostat housing is made different than a Chevy. The groove for the thermostat is in the top housing and if the thermostat moves the housing cracks.
I used adhesive to glue the thermostat to the housing then used adhesive to glue the gasket on then when you set the housing down it doesn't move. Ford OEM thermostats have a clip to hold them in place.
I imagine the housing is cracked.

After starting it last night and getting some pressure on the system, the leaked has stopped for now.

Question though, I have no idea if the jiggle pin is at 12:00. Does that matter at all really? Just may make it difficult to get the air out of the system I'd think.

Thanks to your replies we determined the housing was damaged. There was a small pinhole covered in rust/grime we exposed after a thorough cleaning. A small screw and JB Weld has a temp fix on it now. A new part is $100! May try a salvage yard for a replacement.

Thanks!

If its thin metal you may be able to use a propane torch and solder it if only one hole was observed. It has to be cleaned with soap and water to remove anti freeze deposits. I've patched cracks in radiators this way.