The 240D differential will fit, but the ratio is not the same as the 300D. If I just read the parts catalog correctly, the 300D diff is 1 : 3.46 and the 240D is 1 : 3.69. As stated above, the ratios are stamped on the case.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References