62 steering shaft coupler

Another aftermarket vendor offers a molded rubber boot that fits over the coupler like a second skin. I don't know if that is available for both type couplers.
More importantly is why that cover came off. Getting it to stay in place after servicing/rebuilding the coupling is typical. If human hands didn't cause this issue... something mechanical did. Coupler worn out ? Steering column bearings worn out ? Steering gear loose at K member mounting bolts ?