Keep or Replace Eaton Rear End

[Jahloha]

I have a 1970 C20 with an Eaton rear end. I read everywhere on this site that the Eaton is a rock and if kept taken care of, will last forever.

But

I also read that parts for this rearend are very rare to find and purchase.

So being untaught, what parts are hard to find?

I hoping to do a disc swap on both the front and back...would this resolve the difficulty of finding these parts?

Thanks for the insight.