Resurrecting purely for reference.
Well, as I suspected, the left hand mirror came out in sympathy and failed 6 months or so after the right.
Rather than source another Vee mirror which would likely be old and tired anyway, I took a punt and picked up a breakers yard set from a 2017 DL650. The part code is different but the lever clamps they thread into are unchanged so I figured they'd fit and they looked the same in the photos. Few scrapes on the plastics but the glass is spotless on both and they were less than the 1 Vee mirror I bought before.
They do fit, they are the same size and position mirror but they have a much better attachment and adjustment system at the bottom. Slightly smaller diameter arms and slimmed down bolts/bosses so we'll see if they vibrate any more than the originals but another case of Vee parts becoming rarer but other generations of 650/1000 being readily available.