I have tried several times to install the 10.8.4 update but each time has been unsuccessful. Help?

Greetings,

I have tried several times to update my 27-inch, Mid 2011 iMac from the OS X 10.8.3 (12D78) version of the OS to the "current" listed 10.8.4 version but without success. I follow the standard process of updating the OS through the App Store, the update downloads files, the systems restarts, everything comes back up and the App Store Updates still shows I need to update to 10.8.4. I belive that this is now causing me to miss out on important other updates for my Mac. Any help would be appreciated.

- Michael