Is there any point in repairing/preserving the damaged portion? I was reading this page which, admittedly is advertising products, recommends several steps:
I.e. brush/rubbing off the flaking concrete from the steel rod (I wasn't suggesting a jackhammer on the lintel!!!), removing surface rust with a wire brush and treating metal. It sounds to me like this could be opening a can of worms and I suspect is best left alone...
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