You need a new brake cyclinder as the old one is leaking. You also need a new pair of brake shoes for both sides as you cannot clean the contaminated ones and it's best to renew both axles to get even braking. Clean both drums and brake parts with "brake cleaner" to remove all contaminants. It's best to renew both cylinders together as the nearside one will be worn as well. Renew your brake fluid as well, as it ages it absorbs moisture and reduces efficiency.
Brian
June 2009