The three-week strike by the Canadian Auto Workers in October against General Motors Corp., which ended Oct. 22, cost the company about 90,000 vehicles, nearly a third of which were trucks, estimates Michael Robinet, a market researcher with CSM Forecasting in Farmington, Hills, MI. The remaining two-thirds ranged from the Cadillac DeVille, Seville and Eldorado to the Chevrolet Cavalier and Pontiac Sunfire. In short, the cost was minor compared with last spring's 18-day strike at two Delphi Chassis brake plants in Dayton, Ohio. That strike rippled through the entire North American assembly system much faster and cost about 250,000 units of lost production. The CAW was unable to preserve the pattern it tried to set with Chrysler Corp., which agreed not to sell any Canadian parts plants. But Chrysler has no Canadian parts plants. GM will be allowed to sell a trim plant in Windsor and a stamping plant in Oshawa, Ont., but the new owner will have to recognize the workers' membership in the CAW and honor the agreement reached by the union and GM.