Recently I made the mistake of ordering Bosch O2 sensors from http://www.autopartsauthority.com
I checked the Bosch web site and copied down the part numbers (front and rear) for my 2000 Forester. I verified them with the autoparts web site. Low and behold the part numbers at Bosch and autoparts were INCORRECT. My mechanic ended up getting the front sensor from Subaru.
Autoparts gave me 2 RMA's and 2 return addresses. When I questioned why 2 RMA's and 2 return addresses I was told that theautopartsauthority only TAKES orders; they do not actually stock the parts! Since the parts came from 2 different vendors who actually stocked the items I had to shell out for 2 return packages instead of 1.
BEWARE OF THIS VENDOR.