Wobbly door mirror

The nearside door mirror was held on with electrician’s tape when we bought our Prius, so we peeled it off to discover that two of the three threaded mounts inside had broken off. We tried to glue the fractured piece back in position, but it was a long shot and it failed once we attempted to tighten one of the bolts. We did, however, manage to refit one of the mounting bolts that was missing, but had to resort to tape again. We tested the Prius on the M62 at 70mph and the door mirror doesn’t shake any more.