For a semi-temporary fix, you may look into Eternabond tape. Search the forums for more info.
Your problem sounds like contact corrosion. Either something chemical in your repair reacts directly with the aluminum, or there is some water leak involved, or there is some metal (steel?) in direct contact with the siding behind the problematic area, or any combination of these. You need to find the root cause. A layer of plastic, or some tape or self-.adhesive plastic foil on the back of the siding may stop the process. But without knowing the root cause, you can not be sure.