Turbo problems

["Gorman, Ken (PA62)" <Ken.Gorman@ftw1.honeywell.com>]

I have a 1990 Audi 200 Turbo.  Recently, it lacks power and has little
boost.  After inspecting all the vacuum lines and trying the minor
things, i.e. oil change, fuel filter, air filter, spark plugs, etc. I
ventured further.  It appears as if the impeller on the turbo doesn't
spin.  This may be a case of oil coking on the shaft.

What are my options?

Is it possible to soak the turbo to remove the oil deposits?  
Would an oil change with synthetic oil combined with an aftermarket
additive to remove deposits help?
Would a few light taps on the turbo cause the impeller to break free and
spin?

-or-

Should I have the turbo replaced along with the all the oil lines that
feed it?  What I'm thinking is that if the heat was high enough to coke
the oil on the impeller shaft, the oil lines may be clogged as well.

The car has 140,000 miles on it.  What is the life expectancy for an
Audi Turbo from 1990.  The car has both an electric radiator fan and an
electric coolant pump which both come on after the car is shut-off.  I
thought these improvements kept the temperature of the engine lower,
thus eliminating the need to idle after extended use.

note: I rarely idle the car after hard use.

What is the approximate cost of a turbo?  I've got quotes of 1600 from
the Audi dealer, however, I would imagine there are many aftermarket
alternatives in the 400-600 price range.  Is it reasonable for me to
assume that I can get a turbo for $400-$600?

What are the typical labor installation charges to install a new turbo?
I am a weekend mechanic and am capable for minor jobs (brakes, oil
changes, hoses, etc.) however, the replacement of a turbo is way beyond
my capabilities.

Any advice you could give would be most appreciated.

Regards,

Ken
Ken Gorman
Honeywell, Inc. - Industrial Automation and Control
1100 Virginia Drive - Mail Stop 105
Fort Washington, PA  19034
Phone (215) 641-3390    Fax (215) 641-3850
e-mail: Ken.Gorman@iac.honeywell.com