Dianne,  I think what you are looking for is Lecithin.  Lecithin is a
phospholipid composed of glycerol, 2 fatty acids, phosphate and choline. It
can be purchased at most health food stores.  Dr. Ruth Lawrence suggests
that  a mother with recurring plugged ducts reduce her intake of saturated
fats, increase intake of polyunsaturated fats and take one tablespoon of
lecithin per day (Breastfeeding Answer Book, 1991 ed. p142; Breastfeeding, A
guide for the medical profession, 3rd ed. p.205)--sorry, my more recent
editions are at work!  I've had mothers with this problem respond well to
this management.
Hope this helps,

Genevieve Courant MSc, RN, IBCLC
Sudbury, Ontario  Canada