the evaporator cores on my '92 400SE is in need for replacement?? Any signs that I should be aware of??

Take your car back to dealer or find a good expericnce shop to replace evaporator this job takes a lot time and cost is expensive
$$$$ also check with dealer may be they will
(good will) part of the cost.
hope this help.

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MB STARS Master Guild Technician,12 years MB tech
5 years independent shop owner

The air will stop cooling and there is usually a funny odor in the car caused by the oil in the system seeping out.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM