99 Silverado driveshaft slip yoke is scoured... How bad is it?

[brizzle]

Basically I was swapping out the u joints for Chevy. The u joints on the transfer case side were completely rusted to powder and when I looked at the slip yoke I noticed it was pretty heavily scoured and the tip looks like it's has burned oil possibly. Now beside some squeaking from the driveshaft I have noticed no issues with my transfer case or 4wd before except for an occasional clunk when engaging 4wd. My question is how bad is my transfer case and what are my options ik I need to replace the slip yoke but how bad is the damage to my transfer case. From the outside I can see no evidence of metal dust and the splines for the output shaft look ok. Any suggestions would be appreciated 

[CamGTP]

The outside of the slip yoke doesn't mean anything other than it's smooth for the sealing surface. A grooved or rough surface can chew up the seal.

 

Honestly just looks like it's been dry and moisture has been inside there to rust up the end of the yoke like that.