Bent pushrod, what is the cause?!

I had 2 on my engine shortly after getting it on the road. My guess is old gummy motor oil. I swapped some out for junk yard ones. Another one bent before the first oil change, replaced again and it's been fine for 5+ years...
I have a full set you can have for shipping if you want from a 71 engine that I took out for a magnum swap. Let me know.

Matt