I see no one answered so I will give it a try. Maybe you can describe the sensor a little better. It might trigger someone's memory.
Maybe you are talking about the oil sensor? Bottom left I believe. I believe it has an O ring but I don't see it in the parts book. You might find one if you had it out.
I wonder if you might have put in too much oil? That seems to be the most common cause of an oil leak. The bike holds 3.3 quarts if you change the filter and oil.
I never had any brake noise form my 1100 V Star. I can only hope the noise will go away once the pads seat in. Did you use Yamaha's pads? If not what kind?