Ethanol is hygroscopic, meaning it absorbs water, if there was moisture in your tank it could have mixed with the fuel and contaminated it. Mixing in fresh fuel may help the situation. However, if fuel was the problem there would probably be misfiring in more than one cylinder, however there's no harm in trying. 

I'd still be concerned about spark, replacing the plug and lead isn't necessarily going to fix that, I'd test for spark and then look at the coil if you aren't getting spark. Once you have verified you have a good spark I would try swapping injectors with another cylinder, if problem follows the injector then you need to try and clean it or replace it, if it follows the cylinder something else is wrong.