In my limited experience with them, I've found that the key for me is to 'pop' them open.

I've broken a tiller arm while trying to open one back up while not on the boat. Likewise with a top casting. However, I knew they worked fine on the boat...

So, when they're off the boat, if I need to open them, I whack the arm with a rubber mallet and they open fine. On the boat I don't have issues, but after breaking the arm I make sure to open them with a quick jerk.

I've seen castings much more used than mine, and the hook on the lower one seems to wear down a bit, making them take less force to pop open and closed.

I've also got 4 used inter rudders -- all of them have some amount of cracking around the hole that broke all the way through on yours. I *think* it's likely common, and happens from trying to steer a bit after raising them.