black crusty-s in hair

Question
Hello!  I have a 2 1/2 year old Cardigan Corgi who I've had for a little over 2 years.  Since I got him he's had this spot on the top of his head where he develops a gritty black crusty mess in his hair, it's a little less than half an inch in diameter and is located on top of his head right next to his ear.  The spot itself KIND of looks like a little raw wound, but it doesn't bleed (that I see), doesn't hurt him, and doesn't have any sort of tumor like quality (it doesn't seem to have a base underneath the skin).  What it does do is secrete something, that dries into a gritty, black crust on his hair. When the hair there is cleaned, you don't notice or feel anything.  He doesn't act lethargic, isn't vomiting,has normal bowel movements; all together quite healthy, except for this one thing.  Which, of course, I am worried is cancer.  Now, I get regular vet check ups, and no one has every said anything about it.  I asked his first vet point black about it, she looked at it and said not to worry.  His second vet noticed it, examined it, and moved on.  Now he is due for his check up, So I figured I'd ask you so I know what to question my vet about (unfortunately I just moved so i have to find a new vet).  Thank you so much for your time and I look forward to your response.

Answer
This sounds like a sebaceous cyst or a small sebaceous adenoma.  There are oil glands surrounding each hair and sometimes one will block up (cyst) and other times, one will become a small tumor (adenoma).  Both can leak this oily secretion onto the skin, causing the dark, granular material.  The best way to treat these is to remove a piece of the skin containing this weepy area.