Though the Megane III mirror fits nicely, the plastic moulding around the bolt threads and wiring harness on the underside of the housing is an entirely different shape.
While this might not seem like a problem, what you probably don't realise is that the Fluence mirrors have a half inch layer of squidgy foam soundproofing between the cap inside on the door and the outside plastic of the mirror, which helps deaden the higher frequency sounds you hear from e.g. the air flowing over the housing at speed.
Because the plastic moulding is different, this soundproofing layer will not fit, so until I can find a Fluence mirror (i.e. bite the bullet and buy one new from Renault
) I'll have to put up with a slightly higher level of noise in the cabin.
Incidentally the mirror I bought from eBay was damaged. Along with three bolts which hold the whole thing to the door, there is in addition a plastic retaining clip at the top of the housing which holds the narrowest portion of the housing against the door frame, preventing it from flapping about.
This had been snapped cleanly in two, meaning it was basically wrestled off the donor vehicle without much patience. I think every similar breaker's yard purchase I've made from eBay has had something similar, so next time I shan't bother. Waste of money.