Don't let this mechanic throw parts at the problem whilst your wallet gets thinner. Like the other posters said search these archives.
Get a second or third opinion too; if no-one else has ideas then take it to a dealership if just to get someone to look at it and give you a quote -you don't have to pay for them to do the eventual work if you don't want.

These cars can be money pits and most mechanics I've found are more than happy to take your cash. It'll probably turn out to be something you can fix yourself.

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1993 320TE M104
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past:

1983 230E W123 M102
1994 E300D S124 OM606 (x2)
1967 250SE W108 M129
1972 280se 3.5 W108 M116
1980 280SE W116 M110
1980 350SE W116 M116
1992 300E W124 M103
1994 E280 W124 M104
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"music and women I cannot but give way to, whatever my business" -Pepys