axle

I have a 2004 Sierra Z71 that is my baby. It has 112k on it and I have used synthetic since day 1. I just did my regular oil change today and when crawling under the truck I noticed some spots that were wet from new oil. One around the drain plug (I figure the plus is just old) the other one(s)...

The diff. in my Suburban is shot. It seems that replacing the entire rear axle assembly will be less costly than fixing or buying another diff. itself. I found a rear axle online and I was just wondering if anyone had an opinion in regards to the credibility of the source I have attached...