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Audi 100 hydraulics (again); the bomb, and the servo

Greetings fellow Audi masochists,

My car ('90 Audi 100) has the following symptoms:
Initially, I could hear a ticking, or perhaps clicking noise, that does
not sound like a typical valve noise.
This noise changed volume, and I think frequency when I step on the
brake pedal.
Later, I started noticing that it takes about 5 or 6 break pedal presses
to activate the red break light (same light used for parking brake
warning).  Now it takes a mere 2 pedal presses to activate the light,
and the pedal has become noticeably firmer.

My hydraulic pump had been replaced about 2 years ago, and it does not
leak.  I think the probability of low pump output is low (however I have
not discounted it).  The remaining high probability items (in my mind)
are the brake servo (is this also called the booster, or is that
something else), and the pressure accumulator (the infamous bomb).

I have seen in the archives someone mentioned that the bomb, when
functional, serves as a natural buffer to smooth hydraulic pump pulses.
Could the ticking noise I am hearing be the pump?

I would be interested in hearing some opinions, given my symptoms, which
I suspect are not atypical ;-)

Is the bomb easy to replace?  (I do have the bentley manual, but it does
not cover any procedures for replacement, just checking; does this mean
replacement is trivial?)

Thanks in advance,

'90 100
'95 Saab 9000 CS (I miss my Audi V6)