Put in my new expansion valve last weekend. Valve costs a whopping $26 but the labor to do the job cost me about 4 hours of my time (it's not worth much anyway). It was pretty tough because it is tucked up in that firewall. There are other threads out there on it. I did not remove the plastic trim. I did undo some of the vacuum lines that were in the way to allow more room for my hands. Used a socket and swivel to remove the 10mm nut, and the 3 mm hex key to remove two bolts that hold the valve in place. It looked like it had a bunch of scale or corrosion inside, but no evidence of metal shavings.

Recharged with DuraCool. Went with it because it is far cheaper than R12 and almost every post I've read speaks of success with the stuff. Get this, one can of it (only 6 oz) was all I put in and I am blowing nice cold air again. You only need about 30% as much of Duracool as you do of R12. Before charging, I vaccumed the system using the Harbor Freight vaccum that you hook to an air compressor, which worked very well.

Air works great now!

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K