All of the dead 128k digital boards in my possession all have various degrees of the same problem: Bit Rot. Particularly the Apple branded RAM chips. There are usually two or more chips which have failed. I have never seen any other failures.
However, I would point out that there are several new resistors on the 512K aside from the mux array which will not match up to the 128k schematic. A search will reveal an extensive discussion about these differences.