this may or may not help...
I went in test mode with ours and did the memory test (or ram test, whatever they call it) and a few of the SIMMs actually showed bad. I wound up pulling all of them out and cleaning the contacts with an eraser, and reinstalled. the following ram test show them all as good. so I'm guessing these boards are at the age where they're dirty.
considering these games are much like a NAOMI GD-ROM where they load the game data in the ram, you might have a corruption somewhere.
beyond that, I don't really know who repairs these.