I ran the Tweaking.com   Windows Repair v2.4.2 on Saturday 3/1/2014 in an attempt to fix the Windows Update failure to update since November 2013.  There were several problems that were fixed but Windows Update was not.  This is on a custom machine with Windows Vista Ultimate at SP2.  This is a 32bit machine.
I downloaded and ran the Hotfix KB947821 successfully, then the Windows Update  again, which failed. I get error code 80073712. 
 I ran the Tweaking windows Repair - option 16 again today, 3/2, with the same results.
fyi I had previously tried the Microsoft Fixit, too, which didn't help.   I found the Windows Update Agent should be 7.6.7600.256 but this has failed since 11/18/2013.  The windows\system32\wuaueng.dll I found on this machine shows 7.4.7600.226 dated 10/27/2009.
I'm gonna need a bigger boat... for this monster problem.  Can you help?
dpctutor
diane - Personal Computer Tutor