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I'm pretty sure that diagram is for 1941 and later. The 1940 oil cap does not look like that.
Correct. The taller tube and front vent facing cap came along in 41 as an effort to improve crankcase ventilation and alleviate sticking or rusting valves. Both could be installed on all engines to get better ventilation into the crankcase. The tube was for raising the cap higher and away from air being blocked and from increased turbulence caused by the oil filter canister which in some circumstances actually created a small suction effect. The cap with the front facing vent was positioned to catch more fan air. 356 engines had a different and more circuitous and restrictive path for air flow thru the crankcase so were more prone to sticking issues than other engines. In addition to the front facing vent opening on the cap, the 356 also got the horizontal vent tube to directly force feed fan air into the cap. It was suggested those items be retrofitted to earlier 356 engines particularly if a customer was an infrequent driver or had issues with sticking valves.
During the war years there were several articles mentioning valve sticking becoming somewhat of a problem on many cars due to the long down times and little driving. In addition to some recommendations about starting the motor periodically and let it come up to operating temp it was also suggested the later cap and higher tube be mentioned to owners for any engines coming into a shop where this might not have already been done. The horizontal tube stayed as only a 356 item.
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