Just unlucky I guess, agree with Paulstris get rid of them. I've had problems in the past with plums going mouldy (my fault, too tight to thin them). This year I've had a wonderful crop (Victoria) only a few showing brown rot, some got slug and snail damage (I've caught the little bu***rs right at the top of the tree!! Not had any problem with wrinkling, though. Must be caused by the fruit drying out, but why? Sorry got no ideas as to cause.