The correct answer is B) low fluid level in the reservoir. Explanation: Overheating of hydraulic fluid in an electro-hydraulic anchor windlass is most commonly caused by a low fluid level in the reservoir. When the fluid level is low, the pump is unable to draw sufficient fluid, leading to cavitation and reduced lubrication, which can cause the fluid to overheat. The other options are less likely to be the primary cause of overheating - low viscosity around the shaft seal, high oil level in the sump, or overload on the pump motor - as these would not directly impact the fluid level and ability of the pump to draw adequate fluid.