You could have a case of "lead streaking" where some iron bit is trapped in a main bearing
and is tearing out extra lead, at some point the iron gets flushed out.
Lead streaking may also lead to high iron numbers too. At the next oil change, take an oil sample,
then add 1 quart kerosene to the oil as the engine idles for 20 minutes, no load, then shut her
down and do an oil and filter change. The idea is kerosene is an engine oil flush, an older trucker trick,
you'll wash out a lot of residual crud you've never seen before, at least I did on a 1980's 318 V8!!
I started using FilterMags on the outside of the spin-on oil filter. Sizes are matched to
filter diameter. I then bought another one, now I run a pair. The iron levels dropped 40%
and the lead dropped with it too. I wish I thought of it decades ago when I used to run
really long distances every year!
Be sure there's 1/2" to 5/8" clearance all they way around your oil filter diameter
if you want to use a pair of FilterMags before buying.
Check out the results and other ideas:
" FILTERMAG vs HOMEBREW "https://app.box.com/s/uxvu8dmscf5wcgftutdm0ejqwgn86tw7
While this does not address the actual root-cause in your case, at least it reduces it until
you do find the root cause and fix it if it's economic to do so.
In my case I can run 6 months before the oil even starts to darken a little on the dipstick
rather then jet black in 5 weeks!
Post when you find out what it was! Good Luck