It could be a filter in rsyslog cutting out a number, but I guess that is not the case.
I do use Rsyslog both as MT user and at work and have done some mistake over the year.
See my post here on how to configure rsyslog:
http://forum.mikrotik.com/t/tool-using-splunk-to-analyse-mikrotik-logs-4-0-graphing-everything/153043/1