Just replaced mine on my '98 V70 AWD. This is now my second pump. The first was replaced under warranty at 20K miles along with the control valve which had failed and allowed water from backwards exhaust flow to condense and build up and seize the motor. Now the motor is just plain old seized again, but NO water apparent at all, just bad bushings and crappy design. I got my motor at FCP Groton (1 860 445-7345) for $259 plus $5 shipping in state of CT. That is the best price anywhere and they shipped the next day. Swap some pieces over from the old assembly and you are set to go, until the next replacement in 4 years... If you haven't had the check valve replaced, you should do that too, about another $100. Mine is still good.

The air pump only provides a boost of fresh air to the exhaust manifold under cold start conditions (under 55 degrees or so) and then only for a minute or so. It helps heat up the catalytic convertor so that emmissions are reduced. If you ignore the replacement I have heard that you may do harm to the O2 sensor. Some states that query the OBD2 logics in the car as a result of emmissions inspections may fail your car too if a code is set in memory.