Check the replies to my post of 5/3/2001, Icesailor provided a really thorough method of checking for door lock leaks. The post was titled: "82 300TD A/C problem". About the droning noise, my car does that too on the highway, especially at speeds above 75 mph. It doesn't seem to get any worse over time so I assumed that this is a characteristic of the Diesel engine, although I've never asked anyone about it. Oh, to search for the post, just click on the globe(search) icon above.

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Dave
1995 C280
1999 Triumph Daytona 955I - my speed fix.
1982 300TD - Gone, but not forgotten.