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Now I kind of understand the reason to pressurise the crank. To sim it up. It simplifies the need to use hardware to maintain pressure and got rid of the leak problem.

Yes Aviator, with solid sealings, as gaskets and flanges, there is no loss of gas.
When the gas is air, gas leaks are contrasted by a compressor, but it is expensive to build and subtracts power, in the case of specialty gases such as hydrogen or helium, escapes are not eligible.

For Ian,
yes the tube frame of the engine is the reservoir! The frame has to be filled by compressed air before stops the engine, and allows the followings start.
The start procedure (may be is dowloadable) is not at all simplex.

For Ian,
yes Philips engineers exhumed in 1950 the Stirling engine forgotten for many years, but the engine had good success with that name in 1800.
The reason for the design of the "bungalow set" was the first development of civil aviation in 1930-40, (primarly for postal service) the construction of improvised airfields, without communication equipments, and the need of electricity for tube radio in places (airfields) without net power. For this a small motor cooled by air, and the use of light alloys, to limit the weights. The engines has to be carried on site by plane.

It was in 1937, when Phillips built their first hot air engine, it produced 16W. The project manager wanted a suitablename for the engine type, and picked Stirling. The engineer's name was Rolf Meijer. Ian S C

Thanks Ian, you're very well informed!
I read that with the German occupation of the Belgium, during the war, the prototypes and the drawings were found by German soldiers, but were considered to be related to a strange design of a compressor and were ignored.

I'm not in accord about the name, the use of the name was resumed as was resumed the scheme of the engine.
The brother of Robert Stirling was an engineer and with Robert (the inventor) found a Company that built large engines, called "Stirling Engines" that have at first good commercial success, being the Stirling engines covered by a patent, and yet built for many years, is obvious that this type of engine, when resumed, is called "Stirling"; as we use too.
The failure and abandonment of large engines built by Stirling in 1800 was not due to the operation, or efficiency (however modest), but the lack of materials of the hot cap, built in a poor quality steel in that time available, which required frequent replacement, with loss of time and for so frequent unavailability of the engine.
When better steel became allowable the steam boilers (for steam engines) that became reliable and safe, and they took interest in Stirling.

Been digging a bit more,it seems that in 1884 some one with the name of Fleeming Jenkin suggested that all hot air engines should be called Stirl;ing engines.but that found little favour amoung manufacturers of the time, it was later taken up by Phillips in 1937. In the 1970s Graham Walker suggested stirling should cover exclusively closed cycle, regenerative motors with external heat source.
I don't worry too much what they are called, as long as it is NOT Sterling. Ian S C

If Walker has a necessity to precise this, may there was a lot of confusion; in fact the patent of R. Stirling was only about the regenerator, many hot air engine in closed cycle was yet existing in 1816.
I'm in accortd with you.
Ferraccio