There ARE a small number of Wetzlar-made M4-2s according to literature (Denis Laney's Leica Collectors Guide - the book does not give details of serial numbers, dates of production, etc.).
Originally Posted by Fred Aspen
The whole Wetzlar versus Ontario quality problem was apparently that M Leicas were assembled from parts made to only moderate tolerances and required a lot of input from skilled personnel in terms of trial-and-error fitting of parts, fettling etc. to make them work properly. The appropriate skills were not necessarily at the right level at the start of Canadian production.
Yes, you can experience de-silvering of rangefinder prisms with Leicas of appropriate age (I've had it with an M3 and a postwar IIIc). My repairpeople (Newton Ellis of Liverpool UK) can fix this, the cost was about £100. By and large Leica M2s and M3s are cheaper by an appropriate amount compared with M4 and M6, so a prism repair is by no means uneconomic.