I have been working on several of the 25 rd mags to see what can be done to improve the finish.
I tried a soft cloth and using CLP rubbed the oil into the finish vigorously and then let the mags sit for about an hour.
I came back and then wiped off the excess oil with paper towels. The towels were a black and brown mess. Much of the loose black powdery finish came off.
Once the mags were reasonably clean, I then used an old cloth chamois and lightly buffed the finish by hand. They came out much improved...!!
The finish now is slightly darker / slicker and most of the residue transfer is gone.
It appears if a buyer is willing to spend some time oiling, cleaning and prepping the mags...they may be OK. It's just extra clean up work needed that was not required with previous mags.
Just be prepared to make a mess.