Is this problem due to chain growth on full-sus frames stressing the mechanism?
Well, certainly many people have been running them for years without problems – like you. Conversely a few people keep on having them break – like me!
So, it must be something we’re doing to stress them out! I think the difference between FS and hardtail could be part of it, as the clutch will be ‘working’ every time the chain grows due to suspension movement on a FS, which theoretically has to be 50% of the time.
I also think it has to do with riding style and ‘roughness’ of trail. Not wanting to suggest I’m a gnarlier rider than those who don’t break their clutches (I’m not!) but it is telling to me that both times my clutch broke was in the middle of MTB holidays where I was riding more, and more rocky/bumpy trails than normal.
Finally, I think maintenance has a part to play also, because I’ve noticed that the lube on the clutch band can dry/wear out over time and this increases the tension. If you don’t re-adjust the tension and/or re-lube then this can lead to extra stress on the clutch.
Fact is that whatever causes the extra stress, the cam bracket was the weakest link and was the part to fail. Hopefully now Shimano have strengthened that part, even if your riding style/type of bike/trails are more stressful for the clutch, it shouldn’t result in failure anymore.