If I had the answer to this i'd be a millionaire!
I can sympathize, Bracken has one of those impossible coats.
You can try giving him a vinegar rinse after a bath (oatmeal or medicated shampoo- a coal tar/sulphur/salicylic acid shampoo is a good place to start) you can do up to 50% vinegar to 50% water; then putting him up in a heavier oil such as Shaws or Plush Puppy (skirt , feathering, ears only!
)