Is there any reason why Lock Shop would not have Mercedes Key Blanks that are not solid Metal?
I bought several Key Blanks on Ebay that are Nickle Plated Brass no plastic on them. They have Embossed on them "For Mercedes" on one side and "MB41" on the other.
No makers name on them.

Later when I needed another trunk key for my Volvo I went to the Volvo dealer as none of the local places had them. The Volvo Dealer directed me to a lock shop down the street from them.
I ask them about Mercedes keys and they had them.

Of coures you need a good Key for them to copy from.

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84 300D, 82 Volvo 244Gl Diesel