Large Starter

OK. I have a 68 valiant 100 that has a 318 engine from a 74 dart. Has been converted to electronic ign for 10 years now. The starter finally went out 6 months ago after 14 years. I took it into AZ (Auto Zone) for a new super torque one 59.99. Took me a long time to put it in due to headers. After 3 wks the starter did not start, All it did was clack. I tried jumping it from both poles at starter and starter relay and "Clack". Pulled it out and took it in for another one, still under warranty. Put it in, it worked and after another month "clack". What could this be, I believe it is defect rebuilds. Plannig on mini starter. Any reason why this might be happening, thanks. I have':wack:nt been around the thread since 2007 due to two new kids.