Disco 300 TDi rear prop question

Morning all, been a while.

I have a question for Disco guru's.

My Disco developed a vibration from the rear when under acceleration from say 25mph onwards. Thought it may have been the hardy spicer joint so removed the prop and it's spot on. It does however have a rubber doughnut at the back end of the prop that couples the prop to the diff which is perished and looking knackered, so a new one will be fitted. I also noticed that there is a (don't know what you call it) for want of a better description a centralising bush?? that is pressed into the end of the prop that I guess aligns it to the diff input shaft.

What is it?
Can you buy it separately?

Any advice would be great.

Kind regards
Jonathan

Just replace the donut, the spigot can be a biatch to get out sometimes and doesn't do a lot other than centralise .. mine's chewed at the end from an abortive attempt to replace it .. so long as it's central it doesn't matter ..

Cheers for the swift reply Paul, very much appreciated.

Jonathan