Well, after about 9 months of scrolling on my EX21, I noticed my blade tension was not holding. The blade wasn't coming out, just the tension was decreasing. I went by and talked to Ray @Seyco and he said the set screw and the thumb screw of the blade holder were worn out. (I took them for him to evaluate just in case). He was right, no problems now. FYI, he said if I did a lot of scrolling. the pair should be changed regularly, about every four months or even sooner; depending on the volume of dust made. He did say they could be taken out and very lightly rubbed with sand paper as long as they were flat. He suggested screwing into a flat piece of wood with only about the 1/64 or less exposed to the sanding belt. But, in my case it was too late, so I had to replace them.
Tony,aka,Toneman