There aren't any O-Rings to replace except for the one that you put into the engine block when installing the water pump (which has you taking out the water pump anyway). I have a good working one from a new/used engine install that I swapped out thinking I had a water pump problem but didn't. It's good on the inside and bearing is solid. $60.00 if you want it (Mercedes Benz pump). I bought a new one, installed it, and discovered later that I had a plugged radiator. There is an easy DIY under resources in this forum. A new pump will run about $120.00 and up. It's probably leaking from that O-Ring (my daughter's was really bad and that is where I learned to do the job). You can't see it from below or above but it's wet there. Sound about right?