My dad wants to change the oil in the rear diff of his 1997 k2500 with a 14blt ff. Not a big deal right? the parts guy told him that if he did then the pinion seal would start leaking really bad. It is seeping a little out of it now not enough to reach the ground. is this truth? I’m comfortable changed the fluid and doing the drum brakes for him but messing with the pinion stuff kinda scares me a little. can anyone shed some light on this? Iv been doing some research about it but I know a lot of you guys on here know an awefull lot about these trucks too.