My 91 Sentra has started to leak anti-freeze. It appears to be leaking from the seal in the front of the water pump. So it looks like I need to replace the pump. Should I get a factory one or is there an aftermarket replacement that is better? What else should I replace while I am at it? It looks like a major PITA to replace, anyone got some good pointers? I have 150K miles, is this normal time for the pump to be replaced?