Congratulations,
  You have learned lesson number 1 about Jag dealers -- they don't know
what they are talking about.

I am not particularly familiar with the S-Type, but I am familiar with Jags
and brakes and Brembos.  I have 3 Jags and two of them run Brembo rotors and
pads.  I also have a friend with a 2001 XJR with the Brembo brake system and
it does not squeal.  Squealing of brakes is caused by a vibration of the pad
against the rotor.  It is a common occurrence.

Quality brake pads come with thin metal plates that are called shims that go
between the pad and the piston in the caliper.  In most cases, a sealant is
used between the surface of the shim and the pad itself to absorb the
vibration and eliminate the noise.  Most after market auto parts stores
carry this sealant.  In my own particular case, I simply use silicone
sealant like you would use it seal a bathroom sink -- but with higher heat
properties.  This eliminates the vibration to the point the squealing goes
away.

When the service guy at the Jag dealership sprayed on the compound, he was
simply doing it to make you go away. As you are aware, as soon as the
compound dried and wore off -- the sequel returned.  Squealing has been a
common problem with common solutions for 40+ years  -- since the widespread
use of disk brakes. Most cars have disk brakes.  Stand in a parking lot and
listen to see how many cars squeal as they brake.

At some point, there must have been work done to the front brakes of your
S-Type.  Apparently, who ever did this work, forgot to replace the shims or
forgot to use the anti-squeal compound on the shims/pads.  If you have NOT
had work done on the front brakes of this car,   then the chances are -- you
need to.  Squealing is sometimes a method of letting the driver know the
pads are getting low.

Now you know why I have 3 Jaguars and not one of them has ever darkened the
service bay of the local dealership.

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