Brake Pressure Metering Valve 1993 Cadillac Deville

Does anyone know what this is?
My father-in-law called me up asking me if I could find one for his 1993 Cadillac Deville 4.9L V8.
He said he was quoted $688 for it, but I don't have a clue what it is.
By the way he describes it to me, it sounds like a Master Cylinder, but I have never heard of one being that much.
Does anyone have any ideas??
BTW, I live in Texas, and he is in Florida, so it makes it even harder since I cannot SEE the part he is talking about..
Hmmm
 

Any ideas would be GREAT!
Thanks in advance! from that price range it sounds like an ABS pump. That is just a guess though. Have him send a pic. Unless the price is parts and labor, then it may be the metering(proportioning) valve. Still just a guess. Hi ARMYtango, Looking in the shop manual it looks like he ment brake pressure modulator valve and that is the hydrolic valve assembly that has the electric motor and the 4 brake lines to it and is mounted low behind the LF headlamp assembly. Your right in that it is tough to know what the part is if you are unable to see it or unfamillar with the name of the part. Hope that helps. Bill willnick..
thanks for the help, I will call him tomorrow and ask him..thanks too for the location! now I will be better able to find it.
I looked up a metering valve and this it what I found out..
A metering valve or "hold off valve" is used in the disc portion of a disc/drum system to hold off the application of the front discs slightly allowing the slower reacting rears to catch up. This provides rear stability on wet surfaces and reduces excessive pad wear.
BUT...I have only found this to be on older cars...such as 1960's models...

hmmm...I will check that out...Thanks again!!