Ongoing Mercedes 1996 C250 (Diesal) Coolant Loss

Despite new coolant system cap and coolant renewal as reported earlier and curing collapsing hose condition a leak has become evident in heater region. On standing and cooling, sometimes a half cup of coolant may
trickle away, running off the bodywork behind the left hand front wheel. Peering down through the maze of bits and pieces under the plastic covered components on the left hand side (looking forward) I can see some green puddling. Armed with a mirror and light maybe the offending spot can be located? No coolant loss occurs during normal use - only after standing and cooling. Very hard to see even where heater plumbing runs. Note a mention of o-ringed seals in the heater region - could one of these have been disrupted due to the vacuums created with the cap problem. Would love to sniff out this probably minor problem without succumbing to the open cheque book approach. Pump seal not suspected now either but a good pointer from a respondent also. Any further advice appreciated and many thanks for previous assistance.
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The cooling system's major stress occurs upon hot engine shut down for the coolant stops circulating and so being cooled by the radiator. Coolant often briefly boils inside the cylinder head and so puts maximum pressure on the cooling system - thus the leak at this time.
The only way to find a coolant leak is to trace it back to its source. No short cuts.
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As a general observation any leakage is generally quite a period (hours) after shut down which is mysterious. Plan to thoroughly search down below with a bulb and mirror - should be visible one would think. Watch this space and many thanks for advice thus far.
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It's probably leaking sooner, but puddling somewhere.... When the puddle gets too full, then it probably spills onto the ground.
Just a theory. Marty
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