Well good luck, eric06. I hope you can get it fixed with the least amount of trouble.
exactly the same problems, found the solution on apple support forum.
the answer is to download http://discussions.apple.com/thread.jspa?threadID=1265322&tstart=90
download and run the standalone 10.51 update the secure.log message is caused by the weekly cron task being run and is normall.
Excellent! Reinstalling an update will sometimes fix quirky behaviour. I dunno why, maybe a teeny glitch in the download on the first try or something...