I'm afraid what you'll have to do is measure the fit up on your moto tool and then find someway to measure the fit up on a dremel flex cable. I bet it would work as all those tools are fairly similar.
As for Sears, Thats no surprise at all. I would be surprised if the people there new that they sold a moto tool. I went in the other day to get some woodworking counterbore's . I couldn't fid them so I asked a clerk where they were(I knew they sold them because I had bought them there before)He didn't know and sent me to a different clerk. He didn't know either but brought me a set of spade bits and insisted thats the only bore's they had. Then the manager came and didn't know what I wanted either. He took me to the drill bits and told me about how he was sorry but he had only been in the tools for about 3 YEARS and didn't know things very well yet! I looked around and there were the bits I wanted hanging on the wall.
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Fix it right the first time, use Baling Wire !