I had a terrible time avoiding slamming the nose
wheel down on virtually every landing.

Yes, the Seneca is challenging in this respect, which is why this
explanation is likely to find receptive listeners. However, it
appears that a vertical hard landing would likely put tension on the
downlink rod end, rather than compression. And the rod failed under
compression.

Our other Seneca was damaged similarly a few years ago, when an
instructor allowed a student to come in hot, and the airplane
porpoised. However, the gear structure showed a lot of other damage
besides this rod end.

The best technique in the Seneca is to trim very nose up on final, and
use forward pressure to maintain airspeed. With the trim helping you
as the airspeed bleeds off, you can land the Seneca in a full stall
and gently lower the nose. Most don't do that, though.