There is an astounding amount of information on the internet. Pages like that are out there but the challenge can be finding them. I didn't find that page reference until after reading your original question. In fact, it wasn't until after reading Donny's offer to email a picture that I thought I had previously seen a picture. Google is like the magic lantern for finding this stuff.
Here is an exercise for you to try. The IH part number for the magneto drive seal (the one you asked about) is 251379R91. The Cub FAQ lists a cross reference to National, but not to CR. Exercise: Find the CR number for that seal.
The first trick is to pick out some good key words to search for, in this case "oil seals" is a good start.
Go to http://www.google.com/
and type in "oil seals" (without the quotes).
The name CR stands for "Chicago Rawhide".
If you don't make any wrong turns, you can be at a screen to type in the IH number within 4 clicks from the Google response.