Originally Posted by pusangani
Go to hardware store, plumbing department, buy a pack of Spout o-rings, they usually come in packs of 10 with varying sizes, try replacing the stock ones with some of these, start with one that looks similar to yours and work from there until it no longer leaks.
+1 You can also try farm and car parts stores. I was able to find all the o-rings I needed with the exeption of the fill valve o-ring - too small.
You can also use silicone gasket maker, a thin coating around the offending rubber piece and your leak is history; available at Canadian Tire or others like it...