Intermittent coolant leak

I have a funny leak on my diesel hatchback.

2012 Citroen 1.6 HDI 200k kms with a new used EGR cooler and cleaned dpf. Car runs fine, no power loss, no smoke. Every fuel tank (1000km) I have to top up the coolant expansion tank. No visible leaks. Pressure tested the system cold and hot without any results.

Coolant ends up in the air filter housing. I thought pressure testing would show a crack in the thermostat housing because that is right under where the air intake pipe goes in the filter housing. Hot coolant spraying from there and being sucked in by the engine was my only solution, but pressure testing showed no leaks anywhere. Anyone have any ideas?

By the way car has almost always lost coolant. I bought it with a blown egr cooler a year ago. Then had to replace the caps on the bleeders. Then the constant tension hose clamps had to be replaced because they were so weakened by rust they didn’t hold the hose on tight enough(car has no rust otherwise btw). And funnily enough it has never overheated at least under my ownership.