I did have a rear jack-point rip out on a very rusty Fintail one time.

So far, despite varying amounts of rust on my W123s, all the jack-points have been solid enough to use - even on the left front of my Euro TD, where I had to fabricate a large patch panel for the surrounding rocker. Of course, I'd never work under there without a jack-stand.
With the worst one on my TD, the inner box-section reinforcment for the jack-tube is still very solid.

Happy Motoring, Mark

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DrDKW