If you think you can quickly pull and replace the sensor without draining the system then it would not hurt to try changing just the o-ring.
I would try the new o-ring, refill the system and if it still leaks grab a new sensor from the dealer ($25) tomorrow and replace it without draining the system.
Here is a shot of what a new sensor looks like if you want to see how thick the o-ring should be for reference.
Straight lines are for fast cars...turns are for fast drivers
'04 M3 - track
'06 650i Cab - daily driver
'02 Highlander - kid hauler
'01 330Ci - winter beater
Last edited by Yorgi; 11-06-2011 at 11:07 AM.
Reason: fix link to picture