Delta 33W576PN Push Pop-Up with Overflow, Polished Nickel

We have two of these that are a little over a year old. One of them has not worked correctly for some months. It does not pop back up when you close the drain. I have unscrewed it, but I cannot get it to pop up at all any more. It seems like many here have had the same problem.

We have five of these things, all bought with the house. From the beginning, two held water indefinitely, two leaked slowly, and one hardly impeded the water at all. Four years later, only one still holds water. Although there's an elegance to these things, there are some things that should be noted. First, between the top gasket and the stage the stopper screws into, they gunk up much quicker than the old fashion lever types, and are more of a pain to clean. Second, you're going to get at least a finger wet releasing the drain, if not closing it as well.