Hello and thank you for clicking on this thread.

I am new here and this is my first post. I will do my best to explain my enquiry.

I have a 1986 registered w123, I am going to guess it was one of the last made but I don't know how to check. I am in Bangkok and I am fairly certain this vehicle was put together here in Thailand.

My differential unit has a serious flaw, I can manually turn the prop shaft about 1 fifth of a turn with both rear wheels on the ground and not turning. Yes it does make a clunk when going into drive or reverse and it has a bearing noise when I accelerate. It a 3.69 ratio based on the case stamping.

I have located two potential replacement diff units of the same ratio but they both differ from mine. I can't upload a pic here so I will explain. The two potential replacement units have a collar with 6 bolts that are on/around the driveshaft openings. My unit, still in the car, does not have these, it's just a plain casting.

Bottom line, are these interchangeable?

One seller assures me it'll fit (btw his diff is out of a w116 that I have droce prior to removal and it's a good unit), the other seller removed it from his w123 to fit a 3.92 ratio. He doesn't have an opinion on interchangeability.

Can anyone give me some guidance?

Thank you for reading.