mavericks 10.9.5 downloaded but not installing
@OP: If you have the update... Download it but DONT install it... Go to /Library/Updates and in there is where the update pkg file lives... Copy (don't delete it or cut it) out of there and install manually. Watch the logs.. i.e. note before and after times!

If it asks you to reboot.. Don't... So ti'll probably try and install.. But get the package anyway...

Install that manually...

In steps:


Download and install the update
After installation, don't restart
Drop to terminal or use finder and goto (cmd+shift+g) /Library/Updates
Copy the OS X update to somewhere else i.e. on your desktop
Restart and see if the update worked
If it worked... Stop here :D
If not... Fire up "Console" in Utilities under your applications....
Note the time of the logs under "All Messages"
Install the update by double clicking on it and install it as you would any other pkg file
After the install, reboot.
Go back to console.. Note the end time!!!!
If it worked! Stop here :D
If it didn't work, can you go through the logs and see if anything fails or complains and come back with that?