On closer inspection and removing deposits from negative post this morning, I found that cell closest to post was slightly open. I could see slight discoloring from where open, and that may account for drip to and deposits on post.
i'm wondering: what effect if any does open cell have on the battery??????
Tangentially, Peter, the cat had been put on as a generic by Midas last September. you're right: could restrict exhaust flow, and then screw up engine. I'll monitor it.
Right now, i'm more curious about battery.