Gritty Residue on End of Dip Stick?

So I did some research and decided to use the AMSOIL 0W-20 Signature Series full synthetic oil. This website MOTOR OIL ENGINEERING TEST DATA | 540 RAT - Tech Facts, NOT Myths provides nice numeric data for oil testing, and AMSOIL Signature Series 0W-20 scored number 2 overall, being the best motor oil tested that was used just out of the bottle. Anyway I thought I would give it a go as it said it would last for 25000 miles. So I drove 10,000 miles, changed the filter with a NAPA Platinum, and then drove another 10,000 miles. I then changed the oil at 20,000 miles and sent in a sample to Blackstone, giving me an extra 5000 miles to spare as a safety from the rated number. Here are the results:


As you can see the results show that the oil worked very well. The question I have was why I am seeing some residue on the tip of the dipstick? It only is on the very tip, as if it sank to the bottom. I'm not sure if there is a some kind of recess that residue could get trapped there in the dipstick hole that would remain even after an oil change. It's a very fine grit but it's hard to tell what it is because the amount on the tip is so small. I've seen it there ever since getting my car which had 60K miles when I bought it. It was well treated by the previous owner and I've babied it ever since I got it. I started using Mobil 1 Extended Performance and then switched over to AMSOIL. Anyway I don't think it has anything to do with the oil, because it's been there ever since I owned the car and there was no indication of anything going wrong in the test report. So does anyone know what this residue is? I know it's probably time to clean out the intake and replace spark plugs, so maybe that's related?

 

The oil looks fine, and it's dark since it picks up soot etc. You can't see anything swirling around. Maybe it is carbon build-up.

 

To be honest, it may not be gritty at all. It's hard to describe because it's so fine, but I'll see what I can do. Thanks for the suggestions.