I'm tracking a vibration rattle in a seat and so I looked
at ETKA.  It shows two "guide pieces" (251 881 213) that
go in the rails.  I remember years ago finding some white
plastic pieces like this breaking apart in my '81.  So
I pulled them out and forgot about it.

Should I replace them?  Does it make the seat slide easier?

For my Syncro Westy, I looked at the swivel and found only
two of the "upper guide pieces" (251 881 319), and
no "lower guide pieces" (251 881 320).  Or are the lower
ones underneath the swivel, so I didn't see them.  I should
have 4 of each per seat, correct?  Should I just replace
them all while I'm at it?

Thanks,
Richard