Nevertheless, depending on the rest of the car's rust this is repairable, I'd take it to a frame shop and have them give you a quote, it's not a complicated nor $pendy repair, BT & DT on others before, never a problem if done proper;y .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

That wouldn't faze a hot-rodder, if you see the types of fab's they do. I wouldn't try just welding up the cracks since the metal around it is likely fatigued too, plus it may be brittle steel to begin with. I would weld a plate around it for support, which should be stronger than factory. Clean the exiting metal well and paint with "weld-thru primer" first, to avoid later corrosion. You can use galvanizing spray paint (Ace Hardware). I have used structural steel pieces from Home Depot. Beside being high-strength, it is zinc=coated. That seems to work well with my cheap Harbor Freight non-gas wire-welder since the zinc out-gasses as you weld (vaporizes ~1000 F). Try not to breath the fumes since welders say zinc gives them a head-ache.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Sadly I think I see another crack inversely U shaped. Strange crack formation in a way. I would call it one crack too many. I suspect perhaps too many things are moving. Or flexing under load.

Anyways if the car has been is service for 46 years it is no shame.

In my rustbelt area I sent 1972 114s to the crusher we owned many years ago now for these issues. Even though I can weld properly and do my own work.

THIS!!

Fairly unusual to see the LH side in this condition. Must have taken a helluva whack somewhere in its lifetime. I've seen a few examples of W123 frames cracking on the RH side but that was due to battery acid leakage corroding the metal. Ya see something new every day!

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

I have welded on and used quite a bit of broken large scale farm equipment that suffers much greater stresses than the average automobile. However, this assumes a competent, experienced welder person. I would have it welded and then monitor it. Power wash the heck out of it and have the shop fabricate a small plate to weld over the crack to reinforce it. It broke in the first place because there wasn't enough steel to handle the stress. It did not break in the first 30 years, probably, and only cracked after many years of pulling and pushing. If it is welded correctly and with a bit of reinforcement, it will not crack again. Seems wasteful to scrap the car for this reason.

__________________
DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
11 GLK 350 So far, so good
08 E350 4matic, Love it.
99 E320 too rusted, sold
87 260E Donated to Newgate School
www.Newgateschool.org - check it out.
12 Ford Escape, sold, forgotten
87 300D, sold, what a mistake
06 Passat 2.0T, PITA, sold

Las Vegas NV

Okay in picture number two see the inverse U shaped crack. Partially obscured by the undercoat on one side. Yet certainly is there. You have to find where the extent of that crack is.