As a “temporary” fix I taped the broken cover back in place and it lasted a couple of years like that. DIY changing the replacement genuine Mazda cover I purchased on eBay seemed pretty straightforward from videos I'd seen, assuming I could very carefully pull off the mirror glass to get to the tabs that needed freeing to release the cover. So last month I took the plunge and tried doing it only to find releasing the mirror glass was much much harder than it looked in the videos. It suddenly came loose, shot out of my hand hitting the door window shattering the mirror 
So what initially was just going to be a £50 replacement cover purchased on eBay turned out to be an additional £198 incl VAT for the new mirror glass and £77 incl VAT for the dealer to fit it (I wasn’t going to break this expensive replacement!) i.e. a total of £325. I’m sure the dealer would have supplied and fitted a new cover for no more than £125 if I’d gone down that route when I originally broke it. Hindsight eh.
Lesson learnt the hard way – try dealer for pricing first!
