And already, the sterling engine is getting quite complex, its simplicity, the reason for using it, diminishes.
Further, changing a liquid to a steam gives more energy out then you put in.
And yes, there are designs for a perpetual motion steam engine, if you can make each of its pieces efficient enough.
Funny enough, it is not really the difference in pressure that drives an engine. It is actually the temperature difference. So, you can say that the sterling concept applies to all engines.
I think Cody's Lab or someone put one in a vacuum chamber and it didn't run. So, if you can put it under pressure, it would also run better.
BTW, the 8-cyclinder model in the third video uses water cooling and he made it with scrap parts. And other people have already talked about using magnets to get the electricity.
Of course, they use them on nuclear subs.