The M3, at least according to Erwin Puts, is the only Leica M with an RF that is free of flare. After I get my M2 back, I will look for this "flare". I have never had a problem in the M3.
Erwin Puts' Web Page Explaining Leica M RF Patch flare
Erwin Puts' Web Page Explaining Leica M RF Patch flare