Genuine MV3 and MV4 both have issues with cracking, probably caused by the run flat tyres fitted by BMW.
Yes, they can be repaired.
I have a set of 18" CSL reps from BM Autosport and they're brilliant. Fit and finish is perfect, and after just over a year they still look like new when they're clean. I don't know anyone who has had a problem with the service from Mark, it's always excellent.
Diamond cut wheels are alwys going to be prone to corrosion and damage, just because of how they're made. I don't think genuine BMW wheels would really last any longer.
Just how many Yorkshire sheep can you fit inside one exhaust?