Even though you dried the inside of the cap and the rotor good when done and probably after, check it again.... Many times a little more water still exists inside the dist and will condense again on the inside of the cap. Check real good for any hairline cracks while you are in there tooas they can hold moisture and cause cross or miss fire even though the cap looks dry.A good trick to do is to wrap the dist with an old bread wrapper and close it off when washing an engine, it dosen't make it waterproof but cuts down the amount of water that can get inside the dist.
Dennis