Each grand juror shall attend every session of the grand jury unless excused by the presiding juror. The presiding juror may excuse a grand juror from attending a grand jury session only for a reason which appears to the presiding juror in his or her discretion as good and sufficient cause for the excuse. No business may be transacted at any session of the grand jury at which less than 14 members of the grand jury are in attendance and no indictment may be found by any grand jury unless at least 12 of their number shall concur in the indictment.