Odor in ventilation system

My 99 E320 has developed a problem my repair shop is strugging with. An alcohol or coolant type smell enters the cabin when the ventilation is turned on. No coolant leak was identified with pressure testing.
Dies anyone have experienc ewiththis problem?
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My '97 E320 had a similar odor when its window washer tank was over filled.
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can anyone assist in diagnosing this problem please?

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Are you bothering to read the replys?
Sheesh.
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Your heat exchanger has a leak and if it is not covered by warranty, the labor is very expensive. The entire dashboard must be removed,m etc. I would only have a dealer fix it if covered, otherwise go elsewhere. P.

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