Forgive me if this is redundant, haven't really gone through all the replies as most were food related.
Putting the food issue aside for the moment, or leaving it to others, this does indeed sound like seborrhea.
As usual, i don't want to interfere with your veterinarians on your case in particular, but here's a quick 'what is seborrhea'.
Seborrhea literally means overproduction of hair oil (kind of like 'sebum diarrhea' - sebum is hair oil), but the term is misleading. It actually usually refers to an overly rapid turnover of skin replacement, and can be dry (sicca) where the flakes are skin, or oily (oleosa) where the flakes are hair oil.
There are two aims of treatment - control the seborrhea directly , with frequent anti-seborrheal shampoos, and try to eliminate the cause. The three main causes of seborrhea are chronic skin irritation, hypothyroidism, or idiopathic (no apparent reason), common, for example, in Cockers. This is one condition where the Omega-3s are also quite likely to be helpful. Hope that helps, Dr. Mac