"extra" part in transfer case repair kit?

I ordered both transfer case recall repair kits, but the one I'm referring to is not the one with the driveshaft yoke in it. It's part no. MD772214. It's a 4 piece kit: extra yoke cover, input shaft oil seal, output shaft oil seal, and a giant 0-ring (4" across). The first 3 parts are obvious to me, but I can't figure out where this O-ring is supposed to go. Anybody know?

 

[powerplay]

You need it if you separate the two cases.

 

Awesome! Just what I wanted to know. Thanks!

 

[CP]

Don't bother unless it's leaking from that connection. More opportunity for problems.

 

Oh, I'm totally not bothering w/it. The endpiece shield thingy is fine too, so that's 2 more extra parts. In the recall kit I got none of the parts had part numbers, which is lame. But I figured out which seal is which by the numbers stamped into them, so here they are for posterity's sake:

input seal: ISD 30 45 6 AE part #: MD723202 CAPS #: 30379

output seal: AH1895G part #: MD701430 CAPS #: 30384