When i replied to this thread last fall i was less than two weeks from discovering i needed triple bypass surgery so i was not really thinking straight. After having reread it just now, if the common problem is splitting the nylon friction washer then the most likely cause is excess end play in the worm gear shaft. When under pressure and an attempt is made to turn the key, rather than rotate the pinion gear, the excess end play is allowing the worm gear shaft to walk down the pinion rather than turn it. This has a vice like effect on the washer by squeezing it between the boss on the key shaft and the tuner body. Essentially, what is happening is when turning the key you are closing the gap where the nylon washer is sandwiched between the two tuner components. The fix would be to prevent the key shaft from reducing the gap to the point the washer fails when you attempt to turn the key. Imagine the pinion gear as fixed and what would happen when you rotate the worm gear against the fixed pinion. Depending on the direction you turned the worm it would either push the key further away or draw it closer to the pinion. Two possible causes of failure would be too much end play in the worm shaft or too much binding on the string shaft, or most likely a combination of both if the dimensions of the individual components vary much when produced which is fairly common in low priced (supposedly) precision assemblies. Consistency costs money and the smaller the parts the more critical proper fit becomes. Another solution would be a more crush resistant washer but it would be hard to find a material that could be made that small and act as a brake pad on the key shaft. The most likely result would be sliwly opening the gap, reducing the braking ability of the washer.