+1 on that. Those stop leak products are the things douche bags use to offload a car with problems. It's a band aid fix that doesn't last and comes back to haunt you when you finally decide to do the job properly. Hard to get out of the radiator and cooling system - you practically need to strip everything down and hot tank it to clean it out. A cylinder head isn't a great job for a novice mechanic to tackle but as long as you have a torque wrench and you set the timing belt right, it's only a matter of taking off the manifolds and undoing a handful of head bolts. Better if you had another head waiting to be bolted up.