When racks go bad

[jjs3rd@ix.netcom.com]

All,

I have a 96 90 sport q with 155k on the clock.  I have had the whole front end rebuilt withing the past 4 months but am experiencing some light feel on my steering now.

By this I mean that the steering lacks definition like the power steering is over boosted.

When it first started I noticed that power steering fluid was way down.  I drained and put new audi fluid.  The steering was better after but still light.  

What might it be?  My guesses are:

1 Power steering speed sensor
2 Power steering pump
3 steering rack (ouch hope not)
4 something else

Any ideas on how to further diagnose this?

Thanks all

J