Subtle variations on the paper ballots used in a May primary election in Cuyahoga County made them unreadable to optical scanners, a review released Monday found. It was the county’s first election using Diebold’s touch-screen and optical-scan voting systems. Black lines separating sections on the ballots were thicker on the Cuyahoga ballots than on those used elsewhere in Ohio, and the ovals where voters marked their choices had slightly different locations. Officials had to hand-count more than 18,000 paper ballots from the primary because of inconsistent tabulations by the optical scanners. The final count was delayed for days. A spokesman for Diebold declined to comment until a final report was released.