Tom. I;m glad that you responded. In fact it was the Hitec 425BB that was used. I'm thinking the difference was the linkage setup. When I built the Macchis I wanted internal linkages for the elevator and rudder for the obvious reason. I was able to do this on elevator but to do so ment the control horn is only 3/4" from hinge to clevis. Not really a problem as long as the servo horn is 3/4"  or  shorter.

The 425BB is rated at 57 oz on 6V. The setup on the second Macchi was a 3/4" control horn with a servo horn of 1" with a ball link and stand-off. The result IMO was this reduced the servo power getting to the elevator by 25% thus the servo output was more like 43 oz.. My setup is a Hitec 5645 which is rated at 168 oz and I am using an aluminum arm and steel clevis at 1/2".

What I think actually failed was the arm. My thought is there was enough flex in the arm due to arm length and linkage offset below the arm that the arm itself was twisting. I think that was the cause of the flutter and the flutter caused the arm to break right where the screw for the ball link passed through the arm. When we examined the wreckage the arm was broken but that end of the pushrod was not bent. This tends to make me beleive the arm did not break upon impact.   All theory of course.