The most common thing to fail in the water pump is the seals. The way to note this is when you change oil, it will appear milky. My old Kaw had a sight glass on the side which made it even easier. The seals aren't that expensive, and the metal parts of the pump usually don't need replacing unless the shaft of the pump is scored or worn where the new seals won't seat. Pay attention the the way the old seals are facing when you remove them so the new ones can be installed correctly.