Thought I'd remove the dust cover and when I did that little spring loaded ball bearing popped out and hit the floor....gone forever. Numrich list the part at $10 and is out of stock. Now this little steel ball measures 0.137, so I go to my favorite place for hard to find items, McMaster Carr. Found a bag of 100 for $7.50 item #9528K228, which is about a years supply for me.
In case anyone is interested.
WJ