Buchman is mix, of what i'm not really sure

. He has a fairly short coat and I was using a slicker brush.
Now that I'm looking at him again, the scratches aren't as noticeable anymore.
His coat seems to feel and smell more oily now. I haven't washed him in 4 weeks and didn't end up doing it today since I didn't want to irritate his skin more. I got some oatmeal shampoo and was thinking of washing him tomorrow.