The best degreaser I have found is the prep solvent used prior to painting automobile surfaces. If you intend to weld it up, be aware that specially Aluminum castings must be preheated fairly hot prior to the weld procedure, only to be heated up much higher during the weld. You need to make sure you won't be cooking some adjacent seal beyond usability in the process. The strongest epoxy I have used to date is made by an outfit named Belzona and it's not cheap.
