I am not sure on how MBUSA is handling this problem, but reading about this problem on this site I politely asked my M.B. service advisor if something has been done about it on my cars.
He showed me the work orders for replacing all wiring harnesses on my 104 engines. The work was done while doing routine oil changes and nobody notified me about it, it was just done - no charge.
By the way, the A/C evaporator has not yet died on my W140, and the service advisor told me when asked about it: "don't worry, M.B. honors a seven year no-cost to the owner replacement warranty on W140 evaps, yours should fail before time is up".