Ford Escape / Hybrid :: 2002 3.0L - Thermostat Housing Leak

I set out to do a coolant flush but ran into an increasing number of problems. When I went to replace the thermostat I discovered one of the three bolts would not come out due to the inside thread on the thermostat housing being stripped. I purchased a brand new housing and O-ring.

When I reinstalled the thermostat (also Motorcraft brand) with the above O-ring and attached all the hoses I had a severe leak between the thermostat housing and the intake hose connecter. I diagnosed the problem as the O-ring slipping off of the lip or ledge inside the thermostat housing and not sealing all the way around.

The Motorcraft O-ring seemed like the diameter was too big for the interior lip of the thermostat housing because the ring would pop up on one side whenever I tried to fully seat it on the interior lip. I went to AutoZone and purchased an orange Duralast O-ring, and while it seemed to be a little smaller diameter than the Motorcraft it too slipped off when I tightened down the housing.

I have tried everything, and every time I tightened down the housing I did it very slowly and carefully doing an 1/4 turn at a time with the three bolts but still the O-ring would slip off.