You can see (and hear) the left rear ESC shutting down during this video. I had all sorts of ideas about what was causing this, however after running out of ideas I went through three spare ESC's to find one with similar throttle characteristics to the rest of them and discovered that it’s probably the Esc that’s at fault. So far it’s had one further flight without incident. Ill give it another two test flights this weekend at low altitude and if it works then ill ‘go for it’!
After all, what could possibly go wrong? Ha ha ha!