Differential fluid and magnetic dipstick

[Ragedisorder]

I recently replaced my differential covers on my 2010 RAM 3500 with 9,000 miles on it and noticed the old fluid to be somewhat cloudy/grungy looking from the rear differential. The front liquid was not grungy in appearance.
Due to clearance issues I had to replace the aftermarket with the front OEM cover.
I have driven only about 25 miles since the new rear cover has been in place. I checked the differential dipstick today and noticed that the magnetic portion is covered with what I can only describe as 'black crap' (it isn't silver or metallic in appearance - or purple, as I used Royal Purple as replacement fluid).
Is this something I should be concerned with? How often should I be checking the dipstick for this material and if it continues, how can I determine if it is a problem? I am thinking I will do several short trips and check, see if it reduces over time maybe?
I did note that the OEM cover had a thick coating of grease inside, that was thicker on the front than the rear. I thought maybe the heat in the rear had caused some of this grease to transfer to the fluid in the differential space... it is a weak theory but all I can think of so far.
Appreciate any suggestions, thanks.

 

[AH64ID]

Very interesting, when I first changed my rear diff fluid at 15K it was still clear.



I would watch it for a while. Maybe put some in a canister and show the dealership.

 

[Ragedisorder]

Update - I drove about 20 miles and checked the rear diff - everything looked good, there was one 'spot' of "crap" on the dipstick, but it was very small. I will perform a longer drive tomorrow and post a picture if I get anything on the dipstick.