Double piston top seal flange came off.

I don't think I've ever seen that, but Cottrell cylinders are notorious for pulling the threads on the bottom of single-stage cylinders, especially those on the back of the tip deck on a high rail. They tended to have to exert more downforce when the slip plate aged and they would chatter coming down.

 

I had bought a new truck in 2014 and wouldn't you know it, same thing happened to mine. First load out, I was loading the middle top deck and went to lift it. No go. Top threaded cap came apart.

 

due to the difference is sizes between the piston side and the rod side of the cylinder, you can get a pressure multiplication effect on the rod side of the cylinder which can exert a huge amount of force on the cylinder cap. So if you have anything causing a restriction in the flow of hydraulic fluid out of the rod side, this can cause the cylinder cap to strip the threads and pop goes the cap. This is assuming that the threads on the cylinder and cap were all up to spec.

 

Yeah, this might occur when an uneven loading takes place. Recently my friend's truck has had the same issue with the cylinder cap. On unloading his goods from the truck his threaded cap came apart it also shows a slight bend in the cylinder and the hydraulic fluid flow out of the cylinder. It is very difficult to manage the situation and then replace the cylinder with a new one.