This is a manual for a diesel engine but the transom shield torque value should be the same. Torque spec is on page 23. 80 Nm (57.8 ft. lbs.). This is for the long rubber gasket that goes between the transom shield and the transom.
After reading your question again, not sure which seal you're asking about. The torque spec for the rubber ring seals clamping ring is on page 29. It's 35 Nm (25 ft. lbs.).
