You are correct, the answer is A) overheated motor windings. If an auxiliary diesel engine with an electric starting system cranks very slowly after repeated start attempts, the likely cause is overheated motor windings in the starter motor. Overheating of the motor windings can reduce the starter's ability to provide sufficient cranking power to the engine, resulting in slow or difficult starting. The other answer choices are incorrect because: B) a broken ring gear teeth would prevent the starter from engaging properly, C) low lubricating oil viscosity would not directly affect the starter motor performance, and D) low compression pressure in the engine cylinders would not impact the starter motor itself.