I forgot to ask what model car you have. Most 4AGZEs are distributorless and have twin coils. If so this cannot be your problem however from what you've said about the 'alloy thing perpendicular to the cams with the plug' it sounds like you have a distributor model. The distributor is usually plastic and has five plugs in it. 4 of these plugs connect to the spark plugs and one plugs into the ignition coil. If it only has 4 plugs, each going into the spark plugs you have a distributorless motor.
This leak is not hard to fix (from what i've heard, i've never done it).