Don't know the part #, you could call CRIS and ask a tech. But for ordering the part, this is the person to contact (as of earlier this year, anyway). Although I should warn you I tried for two weeks to talk to her about the same thing (I was going to also try to replace it myself), but only got voicemail, and Lynn did not return my calls or emails. But other people have had no trouble ordering shims and stuff from her. Don't know what I did wrong.
Lynn Badillo
Pentax Division
National Parts Administrator
3500 N. Windsor Dr. Suite-400
Aurora, CO 80011
Ph. (720)988-2653
E-Mail:
lynn.badillo@wildernestlogistics.com