4 year old MPV? I think they had the same motor as my Mystique: 2.5 l V6.
Yes, they eat water pumps if you replace them with the factory unit (plastic blades). Get one with a metal impellor.
Leaking into the motor? How? Sounds like other problems there, like a head gasket. I blew my water pump at 110 km/hr, up hill passing some guy, took a while before I noticed the temp gauge peg. But the mechanic said that no water actually leaves the motor, so not much chance of overheating (unless you drive for an hour or something). No damage to my car, in fact it ran very well after the new water pump was put in

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That 2.5 l V6 is considered to be a very tough motor (unlike the 4 banger in the Contour/Mystique). It was the best part of that car.
If the work was done at a reputable place, there should be a warranty. Nissan dealers warranty their work for 1 year/20,000 km. Check for a warranty (unless you did it yourself).
Some friends of ours have a 4 year old MPV, they will never buy another Mazda as long as they live. Lost of problems with it. Maybe the Ford content?
