> Can someone give me an informed opinion on the necessity of health
> checks in Japan?

Workers must have a medical examination once a year.
See Roudou-Anzen-Eisei-Hou 66jou (roughly as: Workers
Safety and Health Law) #66.

http://www.jil.go.jp/kikaku-qa/hourei/main/4/h3470100000570.html#J066000000
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太田純(Junn Ohta) (株)リコー/新横浜事業所
ohta@sdg.mdd.ricoh.co.jp