Exactly.  Any battery can leak given the right conditions.  The Maxells appear far more prone to doing so, but given the potential for very severe damage I think "remove all PRAM batteries" is the best strategy.  Apple isn't making any more logic boards for these, and even if you can repair the damage it's likely to be a real pain, and the physical appearance of the board will suffer (and as we all know from http://www.folklore.org/StoryView.py?project=Macintosh&story=PC_Board_Esthetics.txt the appearance of a Macintosh logic board is quite important).