front upper control arm bushing sleeve?

[reek]

so I'm to the point of putting a suspension back on my frame off. noticed one of the donor trucks (78)upper control arms had a sleeve on the outside of the REAR bushing. the other truck (92) did not. Online search seems to indicate this is supposed to be there. they don't seem available after market. any idea what they do? are they absolutely necessary? they don't seem substantial enough to give any stability to the control arm.

it's #10 on the diagram

any help appreciated.

 

[crazzywolfie]

my 93 had one when i replaced the upper control arm bushings. i forget whether i put it back on when i re-assembled it. i would guess they are there just in case.