I am a student of Chris Caswell (of Caswell Carnahan fame) and Cormak Gannon (of Orla and the Gasmen) both are amazing bodhran players with very different styles.
Chris also makes bodhrans (along with harps and other instruments) and his advice to me has been olive oil on my newest drum, unitl it's broken in well. (My husband jokes that I should rub it in with a clove of garlic. I say the bodhran itself repels people without any help, thank you.)
Cormak uses water only, never oil, but living in San Francisco his drum benefits from the fog...
So when I'm playing in the city I use a drum that responds well to humid climates, or a synthetic head that doesn't care. Out of town I've loved the results of the olive oil treatment.
Hope this helps--