ZZ plant in distress?

A couple of days ago, I noticed that this leaf was getting a little discolored.




Last night, I noticed that the discolored parts of the leaves were increasingly translucent and seemed to be pooling with brown fluid. Ew!




This is the leaf after the pooling liquid actually burst out of the leaf, dripped down the spine and dried. All the information that I've seen said that Zamioculcas zamiifolia are largely disease and pest resistant and the worst thing that can happen is that they get overwatered and turn yellow. I haven't seen anything about the leaves forming pustules or blisters that then burst and drip brown liquid. Argh. Help!