Just out of interest. FindMyPast has them listed on an outward passenger list.
STRATHAIRD sailed from Tilbury on 23/Jan/1959
Your people are described as Kenneth Leak dob 21/9/1929 Occupation Refrigerator Mechanic.
Rosemary Leak dob7/4/1931 she is described as a Housewife.
Their previous address is given as 115, Swarcliffe Road, Harrogate, Yorks.
They were scheduled to disembark in Sydney