The W124 E300D transmission is pretty weak compared to the more powerful gas engined ones. But live quite well behind the lazy yet smooth OM606.

Some symptoms that dictate quick repair to put into commission again are.

Transmission will not upshift from 1st gear in any forward range = broken governor drive gear

There are quite a few threads here that can lead to a read and maybe saving of money too.

But - if you do get to order a replacement - verify that you are getting a 722.435 transmission model. (I read this no. off the build sheet of my car and the trans also)

the 2.5 turbo 300D also uses a 722.4xx transmission but upshifts earlier. I dont recall its exact model no.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)