cast aluminum welding

["Dunst, Mordecai" <mdunst@smtplink.Coh.ORG>]

     Old(1950's) cast aluminium is fairly porous.  I need to weld a fairly 
     large crack in an otherwise perfectly good casting.  I think that 
     the casting has to be heated for a while to get the old oil/grease out 
     of the casting that it ad/absorbed over the years.  Then a good 
     cleaning prior to TIG welding.
     
     Q) Is this correct?
     
     Q) How much heat and how long?
     
     Q) Is there another way?  (I'm not sure I want burnt oil fumes in
                                my house if I put it in the oven.)
     
     Q) Some one suggested H2SO4 (sulfuric acid etching)?  Any comments?  
     
     TIA
     
     Mordy Dunst
     GASKET WORKS
     Maker of Copper Head Gaskets