Black and Decker opened a plant in Brockville in 1966. Among other product lines, it was the main production facility for the Workmate for both the Canadian and US markets, which was introduced in 1975. At its height in 1980, the plant employed 1100 people. Things began to go south (literally) in 1985, when Workmate production was moved to São Paulo, Brazil under the corporate policies of"updated positioning," "rationalized markets" and "globalization." Manufacturing at Brockville ended completely in January 1998, when 500 people lost their jobs. In November 2011, Stanley-Black & Decker announced the loss of another 42 jobs as distribution operations were being consolidated in Mississauga. I'm not sure if the company has any presence left in Brockville now.
So, my lawnmower has followed the factory that made it into oblivion. There are still others out there who fondly remember the twin-blade electric mowers. See, for example, GardenWeb.
Like me, my father-in-law always kept tool manuals. So, for anyone who's interested, I've scanned and uploaded a copy of the manual: Manual for Black & Decker No. 5740 Electric Lawnmower. Maybe it will help someone else keep their lawnmower running.