Please see my response in the following thread which may provide additional information: Something wrong with first layer!
Yes, I totally agree that the darkening of the lubricant is from the "Mechanical wear" of the two metals (Magnetic Receptacle and Tie Rod Ball End).
My concern, is that on typical treatment of properly chromed material, such rapid oxidization and wear would not take place or would take a lot long to get to that point, especially if well lubricated... Just think of an hydraulic ram for instance or similar apparatus which are typically under a lot more load and stress than our printers.
In my personal opinion, I believe this is a quality issue with the process used to chrome the Ball End which will also show accelerated wear of the balls after about 50hrs or so of use. This is not normal and concerning from a mechanical design point of view and machine performance and reliability. I have also contacted Flux for spares Tie Rod Kit, until the Chroming manufacturing process and design is re-assessed and hopefully resolved.
Please check your Ball Ends and advise how they are wearing and estimated hrs in services... Thanks.