Crankcase seal

it keeps dust and water from entering left cover..
this is one place I would use non hardening gasket sealer to span the gaps where gasket is torn..
At the bottom of the left case cover there is a weep/drain channel that is open to atmosphere at all times..

some may use silicone, can't stand the stuff myself as I have used Permatex form a gasket for decades.

appreciate that great response, certainly much cheaper and faster ordering the gasket sealer. For how long should I let it sit before closing the case

immediately assemble, or not, if you wait it will form a thin skin after time.
a small dab spread with finger will be all you need to avoid excessive squeeze out.

I don't like permatex for most jobs. Form-a-gasket is similar. But both are preferable to silicone!
The paper gaskets are best. But in a pinch, yes I'd go with the other 2.