Howdy, I have pulled the rear suspension and diff out and will be putting new bushings (Poly)in and a new cover gasket on the diff is there anything I need to be paying attention to with the diff when I have it open? I have heard to reuse part of the Diff fluid with the new? Fact or fiction. Thanks in Advance

Fiction: Why would anyone say to put part of the old gear lube back in? It's contaminated with the metal shavings that come from normal wear. If you have it drained and nothing looks like it needs attention (ring gear wear etc.) use new lube when after you seal it up. If your diff has a lot of wear it's going to be even more likely you will have a lot of shavings, might not be a bad idea to spray some cleaner in there to make sure you don't have any crud built up in the case. Be sure to clean off the magnetic drain plug too. You will probably find quite a bit of build up on that, no sense leaving it in there to contaminat the new gear lube.

They said it has something to do with the detergents in the new stuff eating away at the build up, hence causing things to loosen up! So you add the old with the new, I am no genius at this car stuff but that sounded a little Dumb to me.

If you have access to a parts washer clean out the case the best you can, or I guess you could spray brake cleaner in there to dislodge any buildup. Yes, the detergents should clean out any sludge builup, but any metal shavings should go to the bottom of the case, the magnet on the drain plug will attract them and hold them there. I'd go ahead and put only new lube in, but if you don't want to you don't have to. It's your car so you can do whatever you feel is best. I've never heard anyone say to put old in with the new and I've been tinkering with cars for 20 years. Maybe I'm just getting old.....