I have a well rusted 2001 Tahoe 4X4 that started to develop an axle seal leak.....With all the rust I am unable to see any differential case casting numbers or numbers on the tube. The rear cover is a 10 bolt, there is a drain plug in the bottom of the differential case, facing the ground. Can anyone tell me what size ring gear this unit has? The build sheet says GT4-rear axle ratio 3.73 and G80-LOCKING DIFFERENTIAL-REAR AXLE. Thank you!