Welding / repairing tiller gear case

[rims421]

I have a honda frc800 walk behind tiller with a leaking gear case.. The case has a couple of welds that are cracked and leaking oil. Is it possible to repair the welds without splitting the case.
My thought was to drain the oil and attempt to weld it from the outside. I have never tried to weld something like this before and I'm concerned about what effect the oil reisdue left on the inside of the case would have on the weld. The area with the cracks are on the upper section of the case so there won't be any oil pooled in that area. Splitting the whole case looks like it would be quite the PITA and I would like to avoid it if at all posssible. Would it be a good idea to heat the area up first with a torch to burn the oil residue off ?
Any ideas, tips, trick, or suggestions would be greatly appreciated.

 

[Shield Arc]

The case wouldn't happen to be cast aluminum would it? Oil on the backside of something that is going to be Tig welded is a royal PITA! If not aluminum I would drain the oil out anyway, and leave the plug out. Grind a groove in the weld / cracks, and drill a hole at each end of the cracks. Preheat with a torch, then weld it up.

 

[Gary Fowler]

While pre-heating with the oxy-fuel torch, before it gets too hot but at least 350F, hit it with the high pressure oxygen to help burn out that oil. Then weld up with your preferred rod to match metallurgy.