last winter I rebuilt my old car's diff once in Jan, then sold it in March. The guy who bought it from me actually messaged me a few times here asking me what parts I used and how I did it because it was super smooth. He messaged me in July, 7 months later, saying he finally had to rebuild the diff because it got crunchy. And to be honest, when I built that diff, it was only because I cracked a diff ring (how? no clue.) other wise it would have been longer than 7 months. Did I have magic? nope. I followed the video instructions to the letter and it just never seemed to go bad.

Now granted, this is the extreme, but I see NO reason why the average person can't get 2-3 months out of a diff if built and adjusted properly. Unless of course you run on super high bite, then you probably need once a week.

if +jf is around, he can back me up. He bought it from me.

Oh and fwiw, I run on medium bite and always ran my diff medium tightness, never tight.