Re-rivet the foot. I did this a few years ago to my 23.5. Drill out the old ones. You may need to "dress" the base of the mast. By that I mean check the aluminum base and make sure it is very flat. Use a good straight edge held up to the base in various positions. When the rivets are loose, the mast can rock a little back and forth. Over time, this can cause the base of the mast to get a curved base. Take your time and use a file to bring it back to a flat shape. Its very soft metal, and will file down quickly.
If the rivet holes are rounded out, you will need to drill them out and go up a size. They are simple "pop" rivets, and you can get a useable pop rivet tool at Harbor Freight for cheap. I cant remember if I used stainless steel or aluminum rivets. I personally don't think it matters. There is not a lot of force acting on those rivets in normal conditions.
Which window are you talking about, that leaks?