Here is an change in my whistle making process that illustrates little changes I am constantly making in the shop...
Over time I have seen a few of my whistles with cracked outer WAB joints. I believe this is a combination of stress during use (or from sitting down with the whistle in one's pocket) and built-in stress from the interference fit of the parts. The walkabout joints are pretty short for the diameter of the whistle, and so experience more torque on the parts.
Originally I was using a live center to hold the outer end of the part when I turned the tuning slide and walkabout joint OD. This resulted in a nominally straight or parallel OD. As the joint was adjusted, the contact area was increased and decreased, making the joint get tighter as it was closed. This increased the pressure in the joint. Not to a point of failure in the short term, but perhaps it contributed to the long term cracking.
I've been turning without a center for a while now. This allows the material to deflect some while turning. The deflection is greater farther from the chuck. Thus the distal end of the cut will have a slightly larger OD than the proximal end, making for a good seal at the distal end while minimizing the stress on the extreme end of the female joint in use. The trade-off in this approach is a very small amount of yaw in the joint. A fair trade for increased life in the whistle and uniform pressure to tune the whistle regardless of the position of the tuning slide.
One other thing I did a long time ago is to bias the thickness of the joint toward the outer (female) part of the joint. All the cracks I have seen have been in the female part of the joint, so I make them as thick as I can, and allow the male portion to be thinner.
Small things to be sure, but each one improves the breed.