To make a long story short,the spring fell out of the flex shaft and I stepped on it. The damage yielded the spring useless. I found a replacement at McMaster-Carr(mcmaster.com). The spring is .250 OD,
.020 inch wire diameter. and is 20 inches long. The length is too short but the SS compression spring is wound tight and can carefully be streched to 36 inches. I have used the new spring for a short time and it appears to be working fine. The spring is not available from CW without buying the entire shaft assembly ($75 I think) The Part # from McMaster's is 9663K16 and costs $4.30. I'm not recommending it but I think it is worth a try if you need a replacement spring.