97 z28. my rearend has some kind of problem and i need some ideas. while driving in gear it's like a hard grinding sound. raised it up and let it role in 1st gear freely. i can hear sounds like little pieces of debree are getting in the bearing path or something. front seal is leaking( like allways) from what i hear. fluid is a little low, about 1/2-1" underneath hole. oil is very dark and feals to me like it's lost its viscosity ( like old motor oil ) very thin. i know it takes like a 70/95 gear oil and gm additive. is there a way to flush the whole box instead of just opening the pumpkin and adding new gear oil? are their any other things that i should try to do to find out what's going on. anything would be a great help, and thank you in advance.