I can't speak to the W123 models, but I do know that for the W201's, generic hydraulic "brake line" from virtually any auto parts store works perfectly. You will have to bend your own hard line for the proper fit. The cost of the straight sections of line is so low, you can afford to screw one or two up to get the fit right.

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