Well, I crawled under my MT '81 240D and the cast-iron diff-housing is definitely stamped 3.69. However, I noticed the half-shafts are rebuilt replacements.
If this has the type of diff-unit that requires pulling the cover to release the inner axle joints, perhaps a PO went ahead and changed out the gears too. The son of the guy I bought this car from, did work at a Mercedes dealer.
As promised, here is the info on the 5 W123 speedometers I have here in Virginia Beach -

123 542 89 01, 80+ mph, from '82 MT 240D, Decal K=1425
Now installed in my '81 MT 240D.

123 542 62 01, 85 mph, Believed from 240D, Decal K=1425

123 542 63 01, 85 mph, Origin unknown, Decal illegible
(I'm hoping this one is for a non-tubo 300D/TD, so I can try it in my Euro 300TD)

123 542 25 57, 100 mph, Was in my MT 240D, Decal K=1425

123 542 28 57, 120 mph, '84 turbo 300D, Decal K=1200

My other two diesels are up in Alexandria, so I don't have their speedometer numbers handy. Thanks again.


Happy Motoring, Mark

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DrDKW