I think you are just the unlucky (no so badly so) bearer of bad luck. I have used the shaft that Oz speaks of for years. I had a 12 year old plane and they never broke. You may have gotten some softer pushrod by chance. Another thing to do is to support the rod closer to the servo output arm. This will minimize flexing...especially under a load. I actually use 1/8 welding rod and tap that 4-40. It makes for a little thicker material. You can get it at a welding shop for about $4.00 for 5 three foot rods. Also, a 5.8 Sachs is quite a shaker of a motor, so I would support at the servo and each fuse former location. Vibration is a killer.