hey guys, some extra info. It's an euro 380 sel, which I'm sure has the limited slip diff because I drove the car just before it was parted. I'm not sure about the year, but it's somewhere near 1983.

About swapping the diff from a w126 into a w123, its possible it the donor is an early w126. They even have the same housing number. However, the my 300D has a 1:3.46 ratio, while the w126 diff I have has a 1:2.47 ratio LSD. As you can see, the W126 diff is way faster.

I really don't want to loose the actual ratio, as my 300D performs really good as it is. I just want to have the advantages of a LSD as well.

Any idea if I can use the satellite box from the w126 with the crown and pinion from the w123?

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1982 W123 300D NA Euro, 300K Miles, 4-speed manual, 3.46 rear diff, early W126 front brakes, Penta rims with 205/60R15 FH900's, custom fitted (by me) audio system, more to come into the money pit... Soon to be installed: Bilstein HD, R107 front discs and 4-piston calipers, HD Suspension springs, wagon front swaybar.