W/O seeing it I've no clue.
Is the gasket hanging into the runner or missing the flange completely?
What this looks like to me is there is too much stress on the collector flange. This redistributes that stress to the header flange in a forward direction. That lifts the header flange away form the head and causes a leak.
It's the reason for the factory bracket at the collector location.
I know it's the reason I went through 2 Focus Central headers. Both broke the welds at the collector merges. If I had, or if I could have got it to fit, the factory mount they'd of lasted longer.
The other car has some ebay header on it and I know the bottom is leaking near the head. If I lift the collector I can head the leak go away.
Problem is the factory bracket doesn't fit with any aftermarket header. So you have to make a sandwich style.
121,000 members and still no sponsored racing.