You can replace the clutch without removing the compressor or opening the sstem, buy you could buy a whole new compressor, and an upgrade at that for about the same price , so.....
Check these folks out, their price on a new 709 is about the same as a clutch from most places, and that 709 makes my 240 wagon into a freezer ( the 709 is a larger capacity , more efficient compressor than the stock ones, and ironically it puts less load on the engine )
http://www.nostalgicairparts.com/COMPRESSORS.htm
And they have everything else that you might need nd are very helpful
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '82 Mercedes 300SD for sale