Credit to the person who found the cracks and you for reporting it on here JMD. I suspect that your car got through the net for the replacement front wishbones following the very public failure on the Autocar track test in 2012. No recall was ever issued so no way of knowing if they were replaced or not. I don't know if there are any distinguishing features to identify what you have fitted, does anyone here?
I don't remember any similar problems with the front wishbones being mentioned on Talk Morgan before, so the later "upgraded" wishbones should all be OK but still worth a quick check.