This is a bit different. I picked up my early-80s vintage Mini-14 a couple of years ago. Shortly after buying it I took it out to the range and shot 50 rounds of South African surplus 5.56mm ball through it. After the last shot, the bolt jammed in the rear and wouldn't go forward. I also heard a rattling sound when I moved the rifle. I was not pleased.
After getting the gun home and filed stripping it, the gas piston fell out. Considering that the piston in a Mini-14 is a stationary part I was a bit alarmed. It turns out that at some point in the past the gun had been detail stripped but when it was reassembled, the gas port bushing was left out. The GPB does two things: (1) regulates the amount of gas tapped from the barrel. Without it, way too much gas is tapped, which batters the action. (2) The GPB holds the piston in place in the gas block.
Note here that this rifle functioned for 50 rounds missing a very important part of the mechanism. It was being fed way too much gas, causing the action to be worked a lot harder than designed. Yet, it didn't malf until the gas piston finally worked it's way loose.
Since this was a used a gun I had to get the part myself. It was about $4 from Brownell's. Since replacing the GPB I've put 400 - 500 rounds through the gun, largely Wolf 55 grain JHP, and I've not had a single malf. I've used PMI 20 and 30 rounders, plus a few aftermarket cheapy mags. Following the ASB sunset I scored a couple of Ruger factory 20 rounders but haven't been able to test them yet.