When I bought my '82 300D it only came with on key, so I went to the dealer and they made me a new master key (the old one was too worn to copy) and another key. It cost almost $50 Canadian with taxes. The two new keys still feel rough when inserting in the door lock or ignition compared to the old key. They work perfectly fine but even after using one of the new keys since spring it's still not very smooth. In response to your question I think Larry's idea is probably your best bet, but be careful not to damage the key.