Alton chaincase oil seal disc

I am replacing a chewed up oil seal disc assembly. I didn't get a chance to observe if the damaged one sealed adequately as the chain ripped it apart shortly after I got the bike. I have the replacement discs, nylon(?) seal and rivets from Alton. The seal is a loose fit on the mainshaft and wonder whether it will do its job. Thoughts would be appreciated. Thanks in advance.

Is it possible to use the original felt seal?

I found the discs and felt washer do not do the job except to limit the leak to a slight drip or weep. Check this link:

Slick