Unfortunately, the camshaft issue in the twins is real. I have had 4 twins here, a 12/2, 2 x 20/2's and a 25/2. Three of them were from different manufacturers and all four suffered camshaft failure. The 12/2 lasted the longest - around 2,000 hours, the 25/2 the shortest - less than 25 hours. Typically the camshaft breaks where the cam gear pin has been driven through the shaft, but other places certainly are possible. The reason for it is stupidly simple - when the Indians drill the holes through for the cams they do not take the time to make sure the drill bit is centred, this results in an "offset" hole, they then put the cam or gear on the shaft and whale the pin through. This causes stress risers in the metal which eventually develop into a crack and then a complete failure. Some cams may not suffer this fate (just good luck?) others will fall apart quickly. The problem is that you cannot see any signs externally when examining a camshaft - it's all hidden under the cams/gears.