The problem was caused by the threads on the bottom of the king pins not getting lubricated, aggravated by loss of grease through poor seals and wear stripping them. This normally only caused the problem at large steering angles, which were only ever used at low speed. I have seen a Moggie with both front wheels collapsed, but only once in all the time I drove one or took an interest in them. It really wasn't his day...
The method of prevention was to pump fresh grease into the system every thousand miles or every month from when new kingpins and trunnions were fitted. The Marina had better seals on the joints so the grease didn't escape. If you own a moggie, the Marina parts are easily fitted.