D2 Rear main seel

Usually why they leak back there is the rear main bearing is worn and possibly the crank journal too but many times just a new main bearing and new 2B2414 packing will correct the leak problem. When the bearing is worn you can tell where the screw area of the crank rubs the bearing at the rear, (back side) of it,s surface leaving it,s wear.I have seen this problem dozens of times with this type setup at the rear bearing.Most of the older Cat engines had this setup till they went to another type sealing back there,some had a piston ring type sealing and others a lip type seal.

If it's sitting off of level, not running, you will see some leakage even if it's not worn at all. It just can't keep oil in under those conditions.