Ive looked everywhere and i cannot find the name for this part. it is located on the very forward end of the drive shaft where it connects to the gearbox. it is rubber with metal ring. looks like some sort of bushing.

anyway, what is this part, what does it do, and why is it worn??

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Current
2006 E320 CDI, 57K bought at 67K "Liesl"
1986 190E 2.3-16, 198K bought at 56K "Brigitta"
1987 300TD (Chuggin Along), 292K "Friedrich"
1995 E320 Wagon, 200K "Louisa"

Past
1987 300SDL, (sold) 125K, bought for 1$ "Kurt"