I started loosing mine last night. I really hope it is the beginning labor in our cases. I'm 39w 6days.
I like you am overdue, 40w3d tomorrow! I started loosing my mucus plug yesterday afternoon. At my check up on Wednesday I was 1cm dialated, from what I understand you start to loose it once your cervix starts to dialate. But some women can sit at 1 - 3cm for weeks, so labour could still be a while away.. but for us I hope not as we already over due!
I would say it is your mucus plug but not necessarily labor being on its way. I hope it is for you though. Nothing worse than going over your due date. Good luck and I hope for a delivery soon for you :)