Here's a new one made in Korea for $150. If you look at the application list, there are 10 pages of it. GM Chevy, Buick, Oldsmobile, Pontiac, Mercedes .
There is a big demand for a replacement R4 and that is why you can get a new one or a rebuilt so cheap.

New AC Compressor 58228 R4 for 68-93 Buick Chevrolet GMC Mercedes-Benz Oldsmobil | eBay

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked