I may (or may not) have discovered something amiss. I decided to leave that little black AC ring off as I don't use it and sometimes it ends up closed when re-installing the box. So with it off I noticed that I could see the edge of the bottom o-ring of the Boro box. Tomorrow I'll change the o-ring on the bottom of the rba to something a little beefier. Going to examine the bottom of the box around the hole for any cling-ons as well.