Frankly I think WinRAR is the best utility to attempt at fixing RAR files. So chances are if WinRAR isn't fixing it, nothing will. Unless you can get a hold of the respective PAR (parity) file(s) for the RAR file, your best bet is to redownload or to try downloading from a different source. If you can get the PAR files,
SmartPAR is an excellent utility for them.