Hello Grandparipper,
I'm a bit stumped at the moment, it's been over 20+ years since I last opened the chain case.
Basically, every cover has a seal, including the engine-side cover
... it's probably the rubber cord inside.
No, you don't need any additional sealant.
If the case ventilation is working, the chain case will be sealed anyway.
Regards, Bruno

Do you actually have a name?