imalabil, i bought precat Bosch O2 sensors from this ebay seller, part# 13477. $128 free shipping per pair and these O2 sensors are exactly 100% the same the OEM that i pulled out from my X5.
2PC BMW O2 Oxygen Sensor Set FRONT/UPSTREAM Genuine Bosch w/ OEM Plug E46/M54 02 | eBay
These precat O2 sensors took me 25-30 minutes to complete the job. There are 4 wires 1 black, 1 grey and 2 white, making sure you plug new sensors same position of the old sensors.