Tadiran have isolated the MB problem to a couple of components as follows:
"The problems are a result of a specific component (Samsung SRAM) which is out of tolerance. The problem is that this component is used interchangeably with SRAMs from other vendors, and we don't know which systems were shipped with a Samsung SRAM and which were shipped with a different SRAM.

The only way to identify a suspicious motherboard is by visual inspection, checking whether the SRAM used is a Samsung one."

Hope this is of help to anyone with similar problems.

Is Mise.