By the “Functionality is pretty much the same,” do you mean it is reported as being out of date but the manual update reports it is up to date ?

If so you could try this before resorting to a clean reinstall:

  • Avast! Manual Virus Definitions Update Download - avast! Virus Definitions Update - Manual Download VPS Update (virus definitions, vpsupd.exe, approx 42MB). - Save the file to your hard disk, locate where you saved it and double click it and that should carry out the virus definitions update.

Note: Ignore the file name in the images of the page that is displayed after clicking the download link, they are for the main program, not for vpsupd.exe which will be downloaded.