Diesel Injector Seat Cleaning

1976 W115 300D
Do you recommend a specific tool, chemical, or (wire?) brush etc to clean the metal seat where the Diesel injector crush washers mount onto/in the prechamber? There is apparently a thin "film"/spots of thin carbon? very hard carbon in this area that seems to be very hard to completly remove, when attempted to clean this area. Some of this thin film of carbon? appears to remain after wire brushing with a small wire brush. I am looking for the proper tool , chemical and or procedure for cleaning this area.

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