Ask Mr. Smarty Plants

Peaches, plums, cherries and almonds are all "stone fruits" in the genus Prunus, which means they are all susceptible to many of the same diseases and pests. Unfortunately, most of the research materials we could find were for commercial orchard management, rather than the back yard peach tree. Without knowing more about the symptoms your tree has been showing, we can't say what is causing it and what controls might be useful. Some of the disease problems are really scary, and control is listed as "destroying all the trees in the neighborhood of the affected tree." Most members of the Prunus genus have been so extensively hybridized for cultivation that just diagnosing a problem is difficult. We have listed several websites below that deal with various problems with the peach tree. We suggest you read through them and see if any of the symptoms match the problems your tree is having. We also recommend that you go to the website for the Agriculture Program of the Cornell University Cooperative Extension of Suffolk County. There are several links to pest and disease management, plus you can get telephone numbers and website addresses for the office on the home page. Local extension offices are always in a better position to advise on treatments for problems gardeners and growers are having.

Clemson University Education Peach Disease Management - this is mostly about problems in the U.S. southeast, but has some good points that should apply to all peach trees.

Gardener's Supply Co. Peach Tree Borer - these symptoms, sap at the base of the tree, sound very much like what you described.

Govt. of British Columbia Guide to Fruit Tree Sprays for the Home Garden

AllExperts Peach Tree + Pest = Problem