this sounds like seborreah, or seborreahic dermatitis, to me. I've had it all my life, and it sounds just like you describe. Sometimes if my hair and scalp get really dry I will have flakies, but a lot of the time it just builds up on my scalp. It's only in certain spots, too, not all over.
I don't know what to tell you about how to deal with it, other than to say that I've noticed my scalp has been a lot clearer the last couple of weeks since I stopped washing w/shampoo every day. I think a good scalp scrub every day or so really helps, i got one of those little scalp massagers at Walgreens and use it even when I just water or co-wash my hair.