If you can , have the area grit blasted, or sand it down and remove all the rust you can get out. You can place a piece of aluminum under the small holes and use lead to fill them. Or if your not apposed to the use of such things , try duraglass, or some other water proof filler. It all depends on how big the holes are.
Lead won't stick to aluminum and you are just using it to hold the lead in place till it cools.
You don't have much in the way of options without some type of welding equipment.