No, W124 sunvisors will not fit a W123 correctly. They look almost the same, but the W124 visors are too long to fit the recess in the roof and to catch the plastic clip. I bought a pair of W124 visors to replace the tattered visors in my '84 300TD and discovered that they didn't fit when I tried to install them.

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1984 MB 300TD
2003 Subaru WRX