What would cause this dishwasher diffuser part to repeatedly fail?

The diffuser / wash arm support part on my Kenmore dishwasher has failed like clockwork every six months, three times now. This comes as one solid part, with the diffuser blades and support axle fused to the inside of the support shell. The failure is always the same: the diffuser and axle piece separates from the shell and falls into a lower position, which makes the wash arm less stable and less effective.

The machine worked for years before this part failed the first time, but now the replacements only last six months. What could be putting additional stress on the part? Is there something else that could be repaired that might make the diffuser last longer?

The part is Frigidaire # 154367402.

A note about wear and tear visible in the picture: The scoring visible on the bottoms of the diffuser blades happens as a result of the part breaking and ending up in the wrong position, so this wear is unrelated to the root cause of the failure.