charlie, there is a product called "boiler stop leak" available at plumbing supply stores. There are a number of brands and a little difference in how they work. Often times when a new boiler is installed the plumber will pump in a liquid for of this and it will stay in the system, circulating around until a leak developes and then it will collect at the leak and harden when it comes into contact with air. I would let the plumber do this job for you, not because its too difficult but because you need a special pump to put it in the system and by the time you rent one and buy the product it wont really be any less expensive than haveing the plumber do it for you. Probably a 1 hr job for him at the most.