Flushing flakes out of crankcase/oil space

Hey guys, glad to be here!
Just bought a 12,000 mile WR250X and happy as clams with it. Except for one thing: the previous owner didn't seem to change the oil very often, and ran the bike as a commuter (a lot of highway action).
When I changed the oil, it was murky and I could see fine metal flakes in the oil as it swirled/poured into the oil bucket.
I know this is normal for 200 or 400 or even 1,000 miles, but I was wondering if this should be the case at 12,000!

I am changing the oil in 200 miles to get the last bit of junk out, and was thinking about adding some Marvel Mystery Oil / Seafoam to help the engine cough out the last bits of gunk.
Anyone else have a similar experience and want to share any tips? :) I usually baby my things so I'm not quite sure what to make of it all!

Thanks in advance, and I hope this little guy can keep going for the next few years! :)

No need to add anything to the oil (additives are a scam). Just change the oil again soon.