I just got a call from the guy I sold my K100RS 16V to.  Seems that 8 of the bobbins that hold the disc to the disc carrier have gone missing.  These were bobbins that I replaced in 2016 to quiet down a lot of disc rattling. 

I'm not sure how they got loose, I was careful to get the clips in the grooves, but I'm checking them on my present K100RS 16V to make sure they are all there and that the clips that hold them in place are properly in their grooves.

Has anyone else had these bobbins go missing?   Might be a good idea to check them if you have a 16 valve bike.

Keep in mind that there are two different part numbers on the 305mm brake discs bobbins on most variants. Perhaps the incorrect part number was used in some of the holes? I have seen this before, and the catalogue (ETK) isn't clear to the untrained eye.

TWB, after spending the afternoon searching the interweb looking at the MaxBMW parts fiche and replacing the missing bobbins with spares removed from a set of used K1100 rotors what we are able to say is:

There are two different bobbins, one of which BMW has listed as NA.  One has a  counterbore on the front of the center hole and a groove with a ring in it.  There are three of these bobbins on each rotor.  According to MaxBMW they are still available and appear to be intended to control the rattle of the disc and the bobbins.

The bobbins that are NA do not have the groove with the ring, and do not have the counterbore bevel on the front of the center hole.  These bobbins are a looser fit than the others because they don't have the ring.  Each rotor has 9 of these bobbins.

I suspect that the problem of losing bobbins was my fault.  When I installed them three years ago, I did it with the wheel on the bike.  From my experience installing replacements today, I suspect that the washers slipped into the grooves for the clips that hold them in place.  When the clip is installed with the washer in the groove, it's possible to have one leg of the clip in the groove and the other out.  The clip will snap into place just like it would with both legs in the groove.  You have to look close to see that it isn't properly installed.  You can't just snap them into place.

I think the problem is solved with the replacement bobbins.  I carefully made sure that the washers did not get in the grooves, that the clips were correctly in their grooves on the bobbins, and that the bobbins were securely held in the rotor.