I received a few diagnoses that both my front and rear diffs are on their way out, my options are either to rebuild them, or replace them with used parts found at a yard. I don't have the funds to rebuild right now nor do I have the money to pay for labor. I'm pretty experienced with auto repair but never tackled a job this in depth. How do I know if the diffs I pull off of a junk yard car will be the exact same as mine? Do they even have to be? Obviously I'll be looking for one with AWD, same year, model, etc. Are there any tips/tricks to help me out here, thanks!