i ordered the cap. diagram shows cap with washer - sold as such. o-ring is my mistake...believe it is below nut. what i thought was o-ring appears to be 'thread' on shaft of cap. it was split. so i will try the cap and see if it closes. then run dishwasher (not using since rinse agent cap won't close) - staving off, hopefully, purchase of new dishwasher. meantime, thanks for all your assistance. i will research replacement dishwasher, also...while i hand wash for now. i apoligise for my poor understanding and misread of o-ring.