I was wondering since my r4 compressor on my 300sd is noisy and going to die. Did mercedes modify this compressor or would a GM r4 be the same, as I have several of those? If it was modified what was done?

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87 300SDL 220K
85 300SD 218K
82 diesel Chevette 440K
85 subaru 4WD turbo
83 4.1L buick powered cutlass THE TOY