The honey to water ratio I found the best was 9 parts honey to 1 part water. More details on the honey approach can be found in the "Basics of Treating Seborrheic Dermatitis with Raw Honey" post.
Seborrheic dermatitis is heavily correlated with immunosuppression. From what I remember the correlation with SD and AIDS is off the charts, something like 40-80% (study). HIV it's something like 36%. In the general population the percentage is somewhere closer to 3-5%. This is likely to due to suppressed sebum protection from the fungus that causes the SD. (Common superficial fungal infections in immunosuppressed patients).
Let me know if you have any other questiosn. Hope that helps and best of luck!