A/C pressure leak

[Gordy_Schesel at allianzlife.com]

One of my two '91s, the 100,  had a bad A/C compressor two summers ago.  I
had it replaced with a rebuilt Audi compressor and then had the conversion
to R134a done at the same time.  Two things I am unhappy about.

One, the compressor has a loud annoying howl when under load (the vehicle
is in motion, the temp is 80ish or more, and the compressor kicks in).  The
howl lasts until the clutch deactivates the compressor, or whatever makes
the compressor stop working.  I'm telling my local  mechanic, who is not
Audi affiliated,  that this is not normal.  He contends that it is.

The second thing, is that the system won't hold pressure from summer to
summer.  This week, it is back in his shop getting recharged.  The system
has had green dye in it since the conversion.  I have a hard time believing
a pressure leak is so hard to detect, especially with green dye.  And I
have a hard time believing the compressor howl is an acceptable system
noise.

Am I expecting too much of my shop mechanics?  Are they being straight with
me?

Thanks for any similar anecdotes.

gordy in saint paul
'91 200 20v tqa, 106k miles (still R12 and OK)
'91 100 quattro, 196k miles (R134a)