Looks to be a 2B-8836 Lip Type Seal.
http://www.ebay.com/itm/CATERPILLAR-2B-8836-OIL-SEAL-NEW-IN-BOX-/262997018347
The 955 12A is in SIS, so the Cat dealer can look up parts for it unlike the other older equipment.
Leaking where? 2B8836 is the pinion seal.
Sprocket seal is a 5H0389 and gasket 7F5012 (one of each in each seal assembly)