I always took my 300D to Ben's Workshop. As Dan mentioned previously, they are not cheap. However, their track record with diagnosing and repairing the car was perfect. Each time you bring the car in, Ben calls you and chats with you about the repair/service, and what you need to be looking at next, etc. The last time I was there, however, I heard the receptionist telling someone over the phone that they aren't accepting any diesels older than 1990 unless you've previously been to the shop. I don't know how hard and fast this rule is. Pheonix Motor Works is very good, too; they specialize in Volvos, but always have a few older Mercedes in the bays. They are one of only two shops in Austin which will work on the Volvo diesel. I've used them since the mid-1990s and always found their service to be excellent. A friend of mine who has a Peugeot raves about a place called Revolution Motors; apparently they work on Mercedes as well.

Best of luck and welcome to Austin!

-Chris

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Christopher
'06 Mercedes E350 station wagon (silver/black)
'85 Mercedes 300D (black pearl/palomino)
'85 Mercedes 300SD (smoke silver/burgundy)
'79 Cadillac Sedan DeVille

'05 Toyota Camry (because always running is nice)

'85 Mercedes 300D sold back to orig. owner 8-1-06
'84 Volvo 264GL Diesel, owned 2000-2013