As Kjelt tried to caution RichardM I would also doubt that the RAMs are faulty. I would not eagerly replace them first as they do not just go bad on their own. Only two things commonly kill them, static discharge and an out of range power supply. In either of those two cases it is more likely for a static discharge to go through what ever is connected to the keyboard, likewise a power rail disruption or reversal could easily kill everything not just the RAM.
You can measure the resistance of the cruft on the PCB with a multimeter if it is conductive enough.