I noticed this weekend when I was under my car that I have a slight trans fluid leak coming from my speed sensor and im guessing its the ring needs replacing. My question is if I remove the speed sensor is the trans fluid going to drain out? and also what exactly is the function of the speed sensor? and last, there only $25 at Advance Auto, so should I just replace the whole unit?

 

Why waste money on a new sensor if it is working? Just get a new o-ring. If you elevate that part of the car/transmisison, I doubt much fluid will come out when the sensor is removed. The sensor's input is important for shift calculations as well as the speedometer.