I have a couple of W201 "parts cars". Feel free to contact me, and I should be able to cut a lower core support out of one of these cars for you. If you could send a pic showing how much of the support you need, it shouldn't be too tough to cut the part out.

Then you would be left with the need to weld in the "new" support to your existing chassis.

That car must be pretty rusty if the lower core support is falling out. Is there structural rust in other areas (jack points, rear subframe, door pillars?).

SteveM.

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'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
'84 Dodge Rampage diesel - Land Speed Record Holder
'13 Ram 2500 Diesel
'05 Toyota 4Runner