I had what sounds like the same problem to this. Mine happened around 18k miles and started only on the first start of the day during cold weather. Try removing your starter and removing both end caps and cleaning out all of the carbon dust, then lube the bushing with a thin grease. Also clean the armeture with scotch brite. It can be a little tricky reinstalling the brushes so be careful.
I actually bought a spare starter off of ebay so I could swap it out and spend time cleaning the removed one. I have not had to use it in almost 35k miles.
Hope this helps
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