My Bad. Got in a hurry and didn't get the breech totally closed and blew the O-ring out. Luckily it stayed on the probe so I didn't lose it. I Know how they are supposed to be replaced. Watched a Tube video, but my fat fingers can't get in the tiny space in the magazine slot to do that. Tried tweesers but that doesn't work. Am working on a big area with white towels all around so I can chase and find that little black circle after my failed attempts.