Do you have another key you can try? When I bought my TE the previous owner gave two keys. One day the one I had been using regularly just wouldn't work in the ignition anymore. Started using the spare, and got a new one at the dealer. Sometimes the spare would feel a little funny when I was unlocking the door, but it was never a serious problem. Beats rekeying everything if it works.

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Fourings

84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)