To me it looks like something that happens when you use high voltage for benching...seen this reported by phase/LN2 users sometimes. The golden connectors become dark. This has not happened to me so far for using max 1.55V on Corsair water cooler. Are those connectors on the CPU totally burnt or can you carefully rub the burn away, with alcohol for example?

For the rust, it seems obvious spill or have you for example washed the cooler under water before assembling it and letting it fully dry?