20" 468M Wheels replaced due to corrosion

[silverbeemersurfer]

Just thought that I would update on my wheel corrosion issues for those interested.
I know that this topic has been covered before but I cannot find any threads despite searching.
My 2015 F15 X5 3.0D M Sport is now 3 years old just had its end of warranty check and 1st MOT.
I raised a query about corrosion in the centre of the wheels and the centre caps. BMW agreed to replace three of the wheels and all centre caps, the N/S rear being judged as being ok, so a good result.
The Service Advisor did make the comment when I discussed the issue with him and he said that they had had quite a few of these wheel returned under warranty.

[X5Sport]

My new Gran Tourer will have diamond cut wheels (not by choice!) and the Dealer refers to using ‘Metalmate’ at £100 a pop with the new car.  Does it work or is this more snake oil designed to extract money from the unwary?