I need to replace the front two according to my CEL...are they the same part? Also, is the rear one the same, and should I go ahead and replace it as well? Where can I get the best deal on these sensors? Are the universal 3 wire ones OK? Thanks!

 

The front two sensors are the same. The rear is different, there's even a difference between 95-96 and 97-99 location. One of the best deals is : http://www.buyoxygensensors.com/

Many org members have bought from these guys. The Universal 3 wires are fine if you don't mind splicing the three wires into your old wires to utilize the original plugin's, but not any universal o2 sensor, it has to be a Maxima year specific universal basically doesn't have the original plugin.