All of My Keys are Brass Keys for my 84 300D.

When got the Car in 2007 it had only the valet Key. The plated but Brass Key Blanks I got on eBay.
The Key Blank has "For Mercedes" on side and MB41 on the other side.

The local Home Depot could not do them because their Key Machine is automatic and there is a set of Dies they have to have. One die to insert the old Key into and another die to hold the new Blank Key.

ACE hardware had the older Key cutting machine where the new and old key are clamped onto the machine. One out of 2 keys they made did not work.
The one that worked brought my total to 2 keys and was enough to keep mey from worry.

Later I had another Key made at a Lock Smith Shop with my own Key Blank.

When My Key got stuck in the Tumbler it turned out the cause was the innards of the Steering Colum Lock were broken.

Previous to the Steering Colum Lock breaking I had occasionally hosed out the Lock Tumbler with WD-40 to lube and flush out any particles.

When I got the Lock Tumbler out I threw it into the little Harbor Freight jewelry cleaning ultrasonic cleaning thank and a little cloud of particles did come out of it.

That was over 4 years ago. I have had no issues I can attribute to the Keys being brass except that on got bent due to my Wife not sticking the key in far enought and trying to turn it.

Not the little ultrasonic tank was handy to clean small automotive parts in using Pruplr Power or something similar. When the Lid broke on it I bought the Harbor Freight larger ultrasonic cleaning tank.

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84 300D, 82 Volvo 244Gl Diesel