Having worked with metal most of my career I have fouind that most drill presses will do the job milling aluminum. Find someone who has a cross-slide vice and you can get real precise with the movement under the arbor. High temp RTV will last very well and is similar to the production mold material that a local company(Silver Buddy) casts thousands of baits a month from. If you have a problem with it flaking out, a small hole(about 1/8") drilled in the center of the fixed area perpindicular to the patch will give the extra volume of JB or rtv a place to hold and adhere to. Those of us who have made too many mistakes while modifying a mold are hesitant to make it worse by drilling out more material but it does keep the patch in place way longer. Welding with a TIG torch is the only permanant fix and usually requires further working after. Find a local weld shop or vocational school. If the problem is merely to open a hook or wire slot, pressure from big vice or arbor press will indent the soft Al enough to hold the wire/hook in place and if it flashes a little, you can GENTLY tap the area witht the hook/wire in place with a hammer to set a little tighter. A very sharp wood chisel will also cut a nice neat slot but just use hand pressure, if you get too carried away, you will be patching again!