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Bronze plating problems with O6 Tool Steel

Q. My company manufactures and repairs aircraft hydraulic parts. Over the last several months, we have been noticing that our bronze plated parts are being attacked by some sort of chemical reaction that can best be described as black "smudging" and pitting on the bronze plated face. The problem presents itself after the parts have been installed and run on a test stand. The operational environment of the parts is characterized by high rotational speeds and high oil temperatures (225F-240F). We have manufactured these parts for 10 years or so and have just now experienced this issue. We have tried three different plating vendors and have had the same results. This leads me to believe that there may be an issue with the base material (O6 tool Steel). Could the graphite content of the tool steel be drawn to the surface of the part during the etching phase of pretreatment and become included in the bronze plating itself? If so, would this cause an adverse reaction similar to what we have seen? Thanks.

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