2016 Superb 1.6 coolant loss with no visible leak

Hi all,

I have a 2016 Superb Combi 1.6 diesel with DCXA engine. High mileage, currently 460k+ km, all motorway use.

I am using upwards of 1 litre of coolant per week and cannot find any visible signs of a leak.

New reservoir bottle and cap fitted last week, water pump and timing belt replaced 20k km ago.

No white smoke from exhaust so might not be head gasket.

Had coolant system pressure tested by mechanic, no loss of pressure

Could it be EGR cooler?

Coolant leaking and getting burned off somewhere, it's driving me mad..!!

Anyone else with similar issue on same engine?

Thanks in advance

Edited 18 August, 202518 Aug by SB23
Additional info added