I agree to replace the diaphragms. Water in oil is the usual cause of the milky look. Replace the diaphragms as they may have tiny cracks that are not really visible. You might as well have new diaphragms with fresh clean oil, and have a clean start for next year.
I never bothered to replace the top rubber in the dome.
Don't let pump freeze--costly to replace. Cover it with your electric blanket--or whatever you have.