See this thread on Benzworld:

Do you own a 140? IR KEYS NLA, Call MBUSA and post here after doing so! - Mercedes-Benz Forum

Mercedes-Benz USA, LLC.

Customer Assistance Center

1 Mercedes-Benz Drive.

Sandy Springs, GA 30328

Tel: 800-367-6372

Post here or there after you call. Need to light a fire under their asses and the documented way to do this is for owners to call in with their VINs, and complain that keys are NLA.

To be clear, your 140 is a BRICK if your last transponder key fails. ALL KEYS are NLA - remotes, plus the service keys.

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL