help! my bodhran is ill!

[Meaghen Mac Laren (B. Aboussafy)]

Hi. I've got a Walton's bodhran that is several years old. I live in a
semi-desert climate which makes the tension of the skin somewhat of a
worry. I practice alot and use a bit of water on the back to loosen the
skin whilst I play. This past summer I noticed during practice that there
is a spot about the size of my palm in the middle of the drumhead that
sounds, for lack of a better word, dead. It doesn't resonate like the rest
of the skin does. This really worries me since it doesn't seem to be
overly affected when I put water on the back. I rubbed some linseed oil
into the head (on the playing side) and it seemed to help for awhile but
now things seem to be getting back to dead sound in the middle again as if
I never oiled the skin. Does anyone have any idea what is causing this
problem or know how to fix it permanently? I'd hate to have to replace the
skin since I'm not sure where to buy one or how to do it. 

 
				apprehensively,
				  Meaghen Mac Laren
				    Ramsgaard, An Tir