why do trees crack and sap?

this tree is cracking and sapping..i know it will die within a year if i dont find a cure. anyone know what causes this? it is a plum tree. the images are here:
http://picasaweb.google.com/socal.penguin/Tree
thanks in advance
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Try here
http://www.ipm.ucdavis.edu/PMG/r611302811.html
Emilie NorCal
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