OM 642 engine coolant leak

[politomick]

I have a 2017 GLE 350 which has developed a niggling leak which is getting worse 1 litre every couple of thousand miles. Has been in to repairers several times with no cure found.
Although one of hoses from the header tank was replaced
Any help would be appreciated

 

[onefortheroad]

Expansion tank caps ??

 

[politomick]

Expansion tank caps ??

No signs of a leak from the cap

 

[onefortheroad]

No signs of a leak from the cap

They steam when old , you wouldn't see a leak.

 

[malcolm E53 AMG]

It’s not unknown for hoses to go porous which can be very difficult to find there are also a lot of o rings in the cooling system nowadays so the leak might have to get worse before it’s discovered it may even be leaking from the oil cooler in the vee (that’s a big job) so an inspection in there is paramount