Rear Transmission Cup - Driveshaft Donut / ORing / Spacer

Howdy All. Just bought my truck and I get some vibration throughout the truck when accelerating. I looked at the UJoints and they seem good. However the part where the drive shaft goes into the rear of the transmission has a cup. That cup, from the pictures provided, show a spacer or donut or something in it to help minimize that play.?.? How do I get one of these parts? Does it help with vibration? Your thoughts and views are welcome. = )

Eric

 

Below is an arrow pointing at what I need. This is missing on my truck now and I get vibrations upon acceleration. Anyone got one of these laying around?
Eric

 

That's actually the whole slip yoke that slides into the transmission

I can't remember the exact name/part # at the moment (on the go and on my computer i have the part # somewhere)

 

I think the slip yoke is the part that goes from the drive shaft into the transmission. I need the rubber, plastic, composite donut that goes around the slip yoke into the cup on the transmission... ? I think? = ) My arrow in the picture above is touching the black round plastic donut thing I need. = ) I will take pictures of mine as soon as the sun comes up in Arizona. LOL

 

I took it to an Amco and found out this part is just a dust cover. Not a seal, gasket, bushing or donut. = ) Just a seal. Not required to work correctly at all. Anyway.... Anyone got a dust cover? LOL I need one. = )

Eric

 

Did you ever find this part number? = ) I know this is old, I just still need that little rubber thing that goes in the tranny and keeps the dust out. = )

Eric