I am the armorer for a police department here in TX. We have several AR's in service. We use them hard as they are a tool of the trade, not a show piece. Most rifles have been in service 3 years or more. I am seeing a crack developing on the shaft about 1/4 inch forward of the teardrop on the forward assist shaft. The round button foward assist have not developed any problems. It would seem the uneven pressure on the teardrop shaped forward assist causes stress on the forward assist shaft causing it to crack / break.  I have asked all AR's with teardrop foward assist be brought in to be changed.
Anyone else had this issue? Any thoughts from you experts?