striped front planets and blown roller clutch failures are pretty common.
4 pinion planets are preferred when building TFs for high performance applications, and most replace three planet pinions when doing the rebuild. there are different splines on the output shafts and one can easily mis match planets and output shafts. I'm building close to 20 years and I've made the mistake we are all human.
as far as the rear roller clutch failure I agree the loading and unloading the transmission in 1st gear will definitly cause the failure. most are under the impression that bolt in sprags will eliminate the failure but in reality it just saves the case.
Just my .02