We found the D42 a bit to slow that's why we went over to a clamp D63 , we was using the D5's before then and was getting through them a bit quick , but no problems so far with either of the clamps. When you say it's wearing the mixing shaft are you talking about the sides of it cos it's always worn there just in the middle but we used to get a welder to run a few welds up the side. How long (in tonnage) would you say your shafts are wearing out it would be good if you could post a picture up of your mixing shaft