Sometime around 2020, I acquired a 7071 with a faulty "Brain" or "Earthy Processor" board. I spent ages trying to fix it and in the end I just gave up on it, until I saw a topic on EEVBLOG started by Lucas Spitzkopf:
https://www.eevblog.com/forum/repair/solartron-7081-earthy-processor-board-reverse-engineering
describing a two layer replacement PCB he had created for this.
This inspired me to create a four layer replacement board based upon his KiCad schematic, and this is the result.