I have an M6 serial no.1676340 with ERNST LEITZ WETZLAR GMBH engraved on top to the rear between rewinder and hotshoe. I have had constant trouble with the rangefinder focus slipping. Had it serviced by Leica UK and Leica Italy and another guy with Lewis in London. It just keeps slipping out within a month or two of usage. I am not a guy who chucks cameras around. I heard that Leica had cameras made in Canada a few years ago and that they were not up to scratch. I wonder if this is one of them.
I love my Leica, but I'm not expert on the history, and I could be wrong here, but I think the M6 is built in Germany. I think Canadian production ended with the M4 (or maybe M5) back in the early or mid-80's. I have a Canadian built M4-P which I've been very happy with. There are a number of web sites that'll give you Leica history just google Leica Cameras
You listing does not include where you live. If you can easily send your camera to the Leitz factory I would strongly consider doing so. First I would email them with a the facts of the matter and the issue of reliability with the camera. It may be particularly helpful if you can scan and attach your previous repair orders and, were I you, a request that they satisfactorily repair this camera without charge. I would not be surprised if they would do so.
I am not familar enough with Leitz practices to speak with any conviction but I know that Zeiss at their homebase has a service counter and will repair items while you wait..I am sure that there must be some items that they cannot repair on the spot. I have read posting by Contax users of having utilized this service.
I can give you the advise to contact Leica in Solms (Germany). M serie's are very complicated in repair. I also have a reliable address in Nijmegen, the Netherlands.
But after servicing by Leica UK and Italy I can strongly recommend to discuss this in Solms first at all.
M6's were never built in Canada, at least to my knowledge. The only Leicas that were built in Canada that had problems were the early M4-2's. There were apparently numerous problems with the early production of these cameras but it was worked out and later cameras were fine. The M4-P was made in Canada and I think it was the last model built there. I don't know of any production problems with it.