Update: chose a junkyard rear end over rebuilding mine and it actually worked
The pinion bearing in my 2004 Ranger was whining so bad I could hear it over the radio, so I had to pick between a $600 rebuild kit or a $150 rear end out of a wrecked 2006 at the yard in Modesto. I went with the junkyard one and swapped it in over a weekend, and the noise is gone with 4,000 miles on it since. Has anyone else rolled the dice on a used rear end and had it last, or did I just get lucky?