Is this something to worry about? Noticed it on my t-case when I took the rear driveshaft off.

 

Eh I wouldnt worry about it for now....

It's called a "stake nut"

The nut is torqued down to a certain spec and then "staked" in place so it doesnt back off...

Just looks like someone has staked and unstaked that nut quite a few times...

You COULD have a problem getting it off if you need to. Just pick up a new stake nut from the dealer for the next time you take it off and replace it

 

Great, thanks. It didn't look like it would affect anything, but...while I've got it apart...
That's what I wanted to hear!

 

Stake nuts are one time use only. Looks like that thing has been reused many times. It's very possible that it will loosen up, and cause an oil leak or worse. New nuts are only a few bucks at the dealer.