I pulled my rear drivshaft today and when I did the slipyoke seperated from the female end. When it did I found a small 1" round plastic piece with what looked like black plastic strings attached to it. The piece had cracked and fell to the ground when the driveshaft seperated. Is this piece important, and if so do I need to have my driveshaft rebuilt?

 

Maybe you can post a pic?

My guess is that it's not very important. Most likely a cap that once loose could have been destroyed. Maybe even a hunk of what was once grease and now is dried into a plastic type string substance.

If you determine the mystery part actually was once lube, make sure you grease that slip joint on a regular basis from now on. You truck and pocketbook will thank you.