A couple caveats to what other have posted. First, as
@BeezFun mentioned, the use of Blackstone Labs was the first thing I thought about when you mentioned metal in the front axle fluid. I have used those guys for testing the Tranny fluid, Diff Fluid and the Engine oil in my Denali as well as the oil in Grand National. They are a reputable company, very professional and pride themselves in their work.
Second,
@Williy brought up a point that also came to mind. Are you the first owner of this tractor? How many hours were on it when you bought it? Could someone have put something like “Royal Purple” gear oil in the front end, which would be obvious reasoning behind the color. However, this would not explain the metal shavings. After it settles out, if it looks more like a metal milkshake than gear oil that has metal shavings in the bottom of the container, then I would be worried. If it were the latter of the two and this was the first time the oil had been changed, it wouldn’t be a complete shock because of the initial break in of the gears. Add in the fact that you have not been using a ballast box and that only adds more shavings and stress to the front end.
The two big questions I have for you is are your rear tires loaded (Rim Guard or otherwise) and does your front axle have a vent/breather tube (either somewhere at its highest point or built into the dipstick). Having owned both Kubota’s and Deere’s I have had issues with the front axles leaking as a result of high pressure. The recommended gear oil heats up and begins to build pressure within the housing; with nowhere to go it finds the weakest point - the rubber gasket for the wheel bearings - and viola a leak develops. This leak can in turn allow water to enter the housing via rain or moisture build up from the outside ambient air. Since water has a higher boiling point than gear oil and because the two don’t mix well the water will boil off (especially in 4WD), thus increasing the wear on the front end.
I’m not saying this or any of the other things I previously mentioned is your issue, but rather its something to be aware of, especially considering you already have a potential lingering problem.
Did you run any cleaner or new fluid through the front housing? With the front end lifted up, you can add some
new/clean gear oil into the axle housing, slowly rotate the front wheels and then drain it. Do this once or twice to see if there is any additional sediment you may have missed. A couple good neodymium (rare earth) magnets near the drain plugs will help to collect any shavings. This will give you an idea as to how bad the problem is without tearing things apart.
If I had to guess the front axle fluid hasn’t been drained by the dealer and wasn’t changed until now, add the lack of rear ballast during front end work and hopefully that’s the cause for your wear. In either case, sending the fluids off to Blackstone will give you a good idea and basis for your next change.
In the event Kubota doesn’t “feel the need” to warranty this problem, then I would consider that with the cost of the fluid, you could potentially make draining the front axle an “end of year item” - not just for preventive maintenance but also for your peace of mind. Hopefully this helps. Please keep us posted of your results. Most guys post a problem and then never come back to post their results, which could have helped someone else who is in the same or a similar situation.