Built a custom oil pan but now...

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I build a custom oil pan for a project car.  Everything turned out  pretty good BUT now I have a few leaks I just can't seem to fix.Ok let's give some hardware background:Welder: Hobart Handler 140 using .030 wire with a 75/25 mixMaterial: 16 gauge sheet metal.So after I built the pan I filled it up with water and found some leaks not to bad.  So I marked them cleaned up the pan and filled the areas it was leaking.  Went back for test #2same leaks same places, like is they were leaking from the edge of the weld bead (hope that make since).  Took a flapper wheel cleaned up the weld and tried it again, and again, and again.  Grrr I am getting good penetration but I am not burning through the metal or getting over amounts of pooling on the opposite side.  Is the .030 wire to thick?  Should I try a .023 wire?  Should I try a different gas like straight argon?  Or is the MIG just not the correct welder for this situation and I should drop a couple of grand and get a TIG?Any ideas would be appreciated at this point.  I am at the point I will have to build another pan, just tack it up and send it out to a shop for TIG.  But I really want to build it my self, ya know?Ok thanks again.
Reply:Odds are you're getting cold lap where you strike the arc, and that's where it's leaking from.You need to grind back further than where the leak started, feather it out some, and start the weld further back.  You could also weld the inside of the pan.  Or, just take it to a shop and let them finish it up.  I probably would have gone .023 on material that thin, though I never MIG stuff like that to begin with.
Reply:try a o/a torch and some rg45