I mig welded a nut on three times at a touch over 100amps which should of got the penetration I needed and certainly heated the bolt up a fair bit but alas the welds would not hold once I put anything over about 10 - 15nm torque on it. With the current I was a bit worried about overheating the actual axle case and making it brittle, as you can see it's not in the best shape.
I've also heated it with a blow torch hoping to get it out with grips before I went down the welding route. All the other bolts were heated and while stiff came out ok. I tapped them with an m10 x 1.5 to clean them up.
Regards the drilling, yes have ended up drilling off centre but haven't quite gone through the thread. As someone said I think the best I can do here is to fit the new stub axle then use that as a guide for drilling an M10 hole, securely fasten on the other side using a nylock nut and threadlock combined with a touch of silicone to fill the mess where the paper gasket/seal will sit flush to the case
I guess we all have to learn some how and I'm definitely one of those people who learns by mistakes. I'm fairly new to working on the car but have done a number of engine related jobs which have been OK (starter, fuel lift, valve clearances, timing belt etc). This thread is probably hilarious for some people but not so much for me....such is life.