What you should be doing, is swapping the CPUs and ram modules from board to board. With the help of someone who can do some statistical analysis for you, you can quickly pinpoint whether the problem resides in the motherboards, or some CPUs or ram modules, or combinations thereof. Presumably, since the servers are so prone to error at the moment, they will not be doing anything important, allowing you to easily swap stuff around. If you can include in this trial, some identical servers which seem to be working fine, this will greatly speed up the process of apportioning blame.