This is the converter upgrade I would use. Mine has not failed, but I've still planned to replace it for better charging performance. Just haven't pulled the trigger yet.
http://www.bestconverter.com/PD4655TV-55-Amp-Converter-Upgrade-Section-for-WFCO-8955-or-Parallax-7155-Includes-Remote_p_616.html#.V5DhD9jruUk
If you just want to replace with the same thing that is in there now, this is the WFCO replacement board.
http://www.bestconverter.com/8955MBA-Main-Board-Assembly-For-8955-ANP-or-PEC_p_117.html#.V5Dh49jruUk