Here is a little trick I use to diagnose things like this I use a digital non contact thermometer (but you can use your hand) Drive the Vehicle for a long time using the brakes alot. Then check the temps of all the rotors. Be carefull they should be very hot. If you have a cold one (compared to the other three) then that is the wheel that is not working. If you have a very hot one that is the one that is stuck and draging. If they are all the same then a good look at the steering components may be in order. I am a diesel mechanic so I may be wrong ( I am used to air brakes) but a rotor will usually cause a pulseation not a pull. If after all of thiss you still can't find the problem try just removing the front calipers and cleaning where they slide. this is very common and does not require replacing anything. Just the other day I had to install pressure gauges on all the brake chambers ( remmember I work on air brakes) to check brake balance. This may be something you want to try if all else fails. If my memory serves the master cyl has two circuts. One that controls the left front and the right rear and the other one that controls the other two wheels. if you had two wheels cold and two hot this may be something to look at, remmember the fronts should be much hotter than the rears as they do most of the work. Hope this helps.