Graphic Corruption in Armed Police Gallop/Cosmic Cop

[Battlesmurf]

I have one of these tri-layer Irem M72 boards that i *just* purchased from a user here. He's overseas- so that might complicate return shipping- so I'm hoping this is an easy fix or something relatively common with these boards. I know that the top/bottom layer are fine- but the middle layer (the one with the jamma connector) is where the issue *most likely* is. What parts should I check out first? Basically- the ship/sprite graphics have little dots/corruption in them. There are 2 mask roms on the main board. I wouldn't know a cheap board to get to swap out that middle board though.

Thanks for the help!