Based on what you wrote, is the gasket the same thickness as the one removed? The steering arm rides on the worm shaft in a groove and if too close to it, the arm can"t move the steering valve easily to direct oil where it"s needed. With bolts loose it can float. Bolts tight now the arm is too close and it can"t float. You could try a thicker gasket or 2 and see if that helps.