You can handle the expansion valve in an afternoon - I have done it. Here is my writeup:

Removal and Replacement of Expansion Valve

I found a Denso rebuilt two years ago for about $250 on the web, so look carefully for the compressor. It has held up nicely. Did not even have to send in the core!

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)