The spring and detent are fine, as is the drum itself. The shift fork was worn down, but that is more of a symptom than the problem. When I set things up to do the undercut the dogs weren't straight, they had almost a degree of chamfer that under load would push things apart. The undercut so far has solved the problem.
It may be mainly a racing mod, and honestly I just did it because if I was going to pull the motor, it was going to have the best transmission it could. Did I really need it? Probably not. I think for most people it would be a peace of mind mod, not really needed but you know it's as strong as possible.