I beg to differ from your opinion. Battery acid can spread on that motherboard to veeery far locations, it just depends on how Amiga was stored. I just revived one, but it needed new Gary socket and even Paula socket was affected too. About that U12, it's only standard logic "glue" chip, which happen to be first in line to take battery attack. Check out where these pins are connected easily at:
http://www.amigapcb.org/
