Satsuma plum tress
It sounds to me like you have a couple problems going on. The leaf curling is very likely due to aphids--this is a common cause of leaf curling in summer. Look at the back of a curled leaf, and you will probably see small green or brown insects and dark material--frass-insect poop. At this time of year, there is very little to do about it except to use a strong stream of water on the underside of the leaves to knock the tiny soft-bodied insects off the tree--this will kill them. Pesticides are NOT indicated once the leaves have curled. Next year, use one of the pesticides listed in this article from WSU's Hortsense during the season to prevent this from happening. http://hortsense.cahnrs.wsu.edu/Public/FactsheetWeb.aspx?ProblemId=117 Don't over-fertilize your tree, and you may be able to control the infestation by handpicking affected leaves during the summer. Do not use a broad spectrum insecticide, as it will kill the beneficial insects that work in your garden to kill aphids and other pests. Be sure to follow all directions on the label.
The holes in your ripe plums are possibly due to a small fly laying its eggs in the fruit. The Spotted Wing Drosophila (SWD) is very active this time of year in SW Washington, and will spoil raspberries, plums, and other soft fruits. If you cut open one of the affected plums, within a couple hours you will most likely see the tiny, almost hair-like wriggling larvae on the fruit. One thing you can do to slow down the population is to pick the fruit as soon as it is ripe, and pick up and destroy any fruit that has fallen from the tree. Do not compost it--place the fruit in a sealed container and dispose of it in the trash. Vinegar traps (see http://cru.cahe.wsu.edu/CEPublications/FS049E/FS049E.pdf ) can be made to monitor the fly population and help you make decisions about managing the problem. Unfortunately, any insecticide you might want to use is only effective against the adult fly, and the "worms" inside the fruit are not affected. Another concern is that while most of the pesticides listed for SWD have a 7-10 day residual effect, a different product with shorter residual effect should be used closer to when you plant to harvest. Please read what WSU's Hortsense has to say about this for homeowners. http://hortsense.cahnrs.wsu.edu/Public/FactsheetWebPrint.aspx?ProblemId=794