Try locating and buying Whitestar CPU boards. Even Stern don't know the part number !

Yes, many of them are battery damaged.

We are working on a "daughter board" that will sit on top of the RHS which is the most prone to battery damage so you can still use the LHS audio part of the original board as it is mostly surface mount but reliable.

The add-on board will sit on top of the original and hard wire to about 20 points on the original PCB

This is still a long way off at this stage.