The little half moon in the valve cover gasket is held in by pressure of the cover (and a grove in it) and some RTV silicone.
Regarding the oil starvation issue - do an oil change with a semi synthetic and allow it to run for some time (unless its going to explode of course) and see if the knock goes away - it might take some time.
1.5 SOHC engines are EASY to find at almost any local scrap yard - shipping should not be an issue.
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