Last year I purchased an 850 sport wagon. About 2 months afterwards I had to have the main crank seal replaced which ran about $800. This was due to the usual leak that starts to show. It was bad a seal. Then around April another leak started to show, except it was showing leakage at the same spot. Turns out it MAY have been the turbo oil return, had that replaced. I say MAY because the leak continued. This time though, I noticed I was having to refill the brake resivoir every two weeks. The droppings were in fact brake fluid and it wasnt until this past weekend that I got smart and started to look around the brake system. I noticed the tape that was wrapped around the electrical connector to a sensor that screws into the master cylinder was wet. When I touched it was soaked in brake fluid. As it turns out,I have a leaking brake pedal sensor. Now all the manuals I've seen on this car show this sensor is in the brake booster and not screwed into the master cylinder, which it is in my case.

Is there anything to watch for when replacing this sensor? Or can it just be unscrewed and replaced?

 

You can unscrew it and replace it.
Clean the wiring really well.
Also you might want to check and see if the EBD switch recall was ever done on your car.
The dealer will be able to look it up by your Vin# and tell you if it was done.

You might have to Bleed the brakes when you replace it.