I fixed plenty of these when I worked for toyota. What I did to fix it was remove the driveline from the pinion flange and mark the driveline with a paint pen to make sure you put it back together right. Then pull out the slip yolk, clean all the grease out of the slip yolk and splines with a screwdriver handle wrapped in a shop rag that is soaked in brake cleaner. Once all the greas is cleaned off, you can see little chatter marks on the splines. I filed the chatter marks down with a mini triangle shaped file (make sure to only go lengthwise on the splines.) Then I used some valve lapping compound that I thinned out with water and put it all over the splines. I would work the slip yolk in and out of the driveline until it got somewhat smooth and then clean the splines out again with brake cleaner. Then it's time to pack the slipyolk with grease and slide it back together - make sure the zirk fitting is out when you slide it together - grease should get pushed out. Put the zirk fitting back in and go test drive it. I never had anymore issues with those drivelines anymore.
