1992 Power stering pressure hose connection.

My power hose began to leak. First I tighten the line nut. The I remove the hose and see a "O" ring. I replace the "O" ring with a plai rubber "O" ring. and the leak continue. I consifered buying a new pressure hose but seems to me that only a "O" ring is needed but the parts house I use don't list the "O" seprated.